Process for producing aromatic carbonates

ABSTRACT

A process for producing aromatic carbonates, which comprises transesterifying, in the presence of a metal-containing catalyst, a starting material selected from a dialkyl carbonate, an alkyl aryl carbonate and a mixture thereof with a reactant selected from an aromatic monohydroxy compound, an alkyl aryl carbonate and a mixture thereof, characterized in that: at least one type of catalyst-containing liquid is taken out, wherein the catalyst-containing liquid is selected from a portion of a high boiling point reaction mixture obtained by the above transesterification and containing the desired aromatic carbonate and the metal-containing catalyst, and a portion of a liquid catalyst fraction obtained by separating the desired aromatic carbonate from the high boiling point reaction mixture, wherein each portion contains (A) high boiling point substance having a boiling point higher than the boiling point of the produced aromatic carbonate and (B) the metal-containing catalyst; (C) a functional substance capable of reacting with at least one component selected from high boiling point substance (A) and metal-containing catalyst (B) is added to the taken-out catalyst-containing liquid; and the (B)/(C) reaction product is recycled to the reaction system, while withdrawing the (A)/(C) reaction product. By the process of the present invention, the desired aromatic carbonates having high purity can be produced stably for a prolonged period of time.

This application is the national phase under 35 U.S.C. § 371 of PCTInternational Application No. PCT/JP98/04152 which has an internationalfiling date of Sep. 16, 1998, which designated the United States ofAmerica.

BACKGROUND OF THE INVENTION

1. Field of The Invention

The present invention relates to a process for producing aromaticcarbonates. More particularly, the present invention is concerned with aprocess for producing aromatic carbonates, which comprisestransesterifying, in the presence of a metal-containing catalyst, astarting material selected from the group consisting of a dialkylcarbonate, an alkyl aryl carbonate and a mixture thereof with a reactantselected from the group consisting of an aromatic monohydroxy compound,an alkyl aryl carbonate and a mixture thereof, characterized in that:

at least one type of catalyst-containing liquid is taken out,

the catalyst-containing liquid being selected from the group consistingof:

a portion of a high boiling point reaction mixture obtained by the abovetransesterification and containing the desired aromatic carbonate andthe metal-containing catalyst, and

a portion of a liquid catalyst fraction obtained by separating thedesired aromatic carbonate from the high boiling point reaction mixture,

each portion containing (A) high boiling point substance having aboiling point higher than the boiling point of the produced aromaticcarbonate and containing (B) the metal-containing catalyst;

(C) a functional substance capable of reacting with at least onecomponent selected from the group consisting of the high boiling pointsubstance (A) and the metal-containing catalyst (B) is added to thetaken-out catalyst-containing liquid, to thereby obtain at least onereaction product selected from the group consisting of an (A)/(C)reaction product and a (B)/(C) reaction product; and

the (B)/(C) reaction product is recycled to the reaction system, whilewithdrawing the (A)/(C) reaction product.

According to the process of the present invention, disadvantageousphenomena, such as the accumulation of the high boiling point substance(A) in the reaction system which causes the discoloration of an ultimatearomatic polycarbonate (which is produced from an aromatic carbonate),can be prevented without withdrawing the catalyst from the reactionsystem so that the desired aromatic carbonates having high purity can beproduced stably for a prolonged period of time.

2. Prior Art

An aromatic carbonate is useful as a raw material for, e.g., theproduction of an aromatic polycarbonate (whose utility as engineeringplastics has been increasing in recent years) without using poisonousphosgene. With respect to the method for the production of an aromaticcarbonate, a method for producing an aromatic carbonate or an aromaticcarbonate mixture is known, in which a dialkyl carbonate, an alkyl arylcarbonate or a mixture thereof is used as a starting material and anaromatic monohydroxy compound, an alkyl aryl carbonate or a mixturethereof is used as a reactant, and in which a transesterificationreaction is performed between the starting material and the reactant.

However, since this type of transesterification is a reversible reactionin which, moreover, not only is the equilibrium biased toward theoriginal system but the reaction rate is also low, the production of anaromatic carbonate by the above-mentioned method on an industrial scaleis accompanied with great difficulties.

To improve the above-mentioned method, several proposals have been made,most of which relate to the development of a catalyst for increasing thereaction rate. As a catalyst for use in the method for producing analkyl aryl carbonate, a diaryl carbonate or a mixture thereof byreacting a dialkyl carbonate with an aromatic hydroxy compound, therehave been proposed various metal-containing catalysts, which include forexample, a Lewis acid, such as a transition metal halide, or compoundscapable of forming a Lewis acid, [see Unexamined Japanese PatentApplication Laid-Open Specification No. 51-105032, Unexamined JapanesePatent Application Laid-Open Specification No. 56-123948 and UnexaminedJapanese Patent Application Laid-Open Specification No. 56-123949(corresponding to West German Patent Application Publication No.2528412, British Patent No. 1499530 and U.S. Pat. No. 4,182,726)], a tincompound, such as an organotin alkoxide or an organotin oxide[Unexamined Japanese Patent Application Laid-Open Specification No.54-48733 (corresponding to West German Patent Application PublicationNo. 2736062), Unexamined Japanese Patent Application Laid-OpenSpecification No. 54-63023, Unexamined Japanese Patent ApplicationLaid-Open Specification No. 60-169444 (corresponding to U.S. Pat. No.4,554,110 and West German Patent Application Publication No. 3445552),Unexamined Japanese Patent Application Laid-Open Specification No.60-169445 (corresponding to U.S. Pat. No. 4,552,704 and West GermanPatent Application Publication No. 3445555), Unexamined Japanese PatentApplication Laid-Open Specification No. 62-277345, and UnexaminedJapanese Patent Application Laid-Open Specification No. 1-265063(corresponding to European Patent Publication No. 338760 and U.S. Pat.No. 5,034,557)], salts and alkoxides of an alkali metal or an alkalineearth metal (Unexamined Japanese Patent Application Laid-OpenSpecification No. 56-25138), lead compounds (Unexamined Japanese PatentApplication Laid- Open Specification No. 57-176932), complexes of ametal, such as copper, iron or zirconium (Unexamined Japanese PatentApplication Laid-Open Specification No. 57-183745), titanic acid esters[Unexamined Japanese Patent Application Laid-Open Specification No.58-185536 (corresponding to U.S. Pat. No. 4,410,464 and West GermanPatent Application Publication No. 3308921)], a mixture of a Lewis acidand protonic acid [Unexamined Japanese Patent Application Laid-OpenSpecification No. 60-173016 (corresponding to U.S. Pat. No. 4,609,501and West German Patent Application Publication No. 3445553)], a compoundof Sc, Mo, Mn, Bi, Te or the like [Unexamined Japanese PatentApplication Laid-Open Specification No. 1-265064 (corresponding toEuropean Patent Publication No. 0 338 760 A1 and U.S. Pat. No.5,034,557)], and ferric acetate (Unexamined Japanese Patent ApplicationLaid-Open Specification No. 61-172852).

As a catalyst for use in the method for producing a diaryl carbonate bya same-species intermolecular transesterification, wherein an alkyl arylcarbonate is disproportionated to a dialkyl carbonate and a diarylcarbonate, there have been proposed various catalysts, which include forexample, a Lewis acid and a transition metal compound which is capableof forming a Lewis acid [see Unexamined Japanese Patent ApplicationLaid-Open Specification No. 51-75044 (corresponding to West GermanPatent Application Publication No. 2552907 and U.S. Pat. No.4,045,464)], a polymeric tin compound [Unexamined Japanese PatentApplication Laid-Open Specification No. 60-169444 (corresponding to U.S.Pat. No. 4,554,110 and West German Patent Application Publication No.3445552)], a compound represented by the formula R—X(=O)OH (wherein X isselected from Sn and Ti, and R is selected from monovalent hydrocarbonresidues) [Unexamined Japanese Patent Application Laid-OpenSpecification No. 60-169445 (corresponding to U.S. Pat. No. 4,552,704and West German Patent Application Publication No. 3445555)], a mixtureof a Lewis acid and protonic acid [Unexamined Japanese PatentApplication Laid-Open Specification No. 60-173016 (corresponding to U.S.Pat. No. 4,609,501 and West German Patent Application Publication No.3445553)], a lead catalyst [Unexamined Japanese Patent ApplicationLaid-Open Specification No. 1-93560 (corresponding to U.S. Pat. No.5,166,393)], a titanium or zirconium compound (Unexamined JapanesePatent Application Laid-Open Specification No. 1-265062), a tin compound[Unexamined Japanese Patent Application Laid-Open Specification No.1-265063 (corresponding to U.S. Pat. No. 5,034,557 and European PatentPublication No. 0 338 760)], and a compound of Sc, Mo, Mn, Bi, Te or thelike [Unexamined Japanese Patent Application Laid-Open Specification No.1-265064 (corresponding to U.S. Pat. No. 5,034,557 and European PatentPublication No. 0 338 760)].

Another attempt for improving the yield of aromatic carbonates in thesereactions consists in biasing the equilibrium toward the product systemas much as possible, by modifying the mode of the reaction process. Forexample, there have been proposed a method in which by-produced methanolis distilled off together with an azeotrope forming agent by azeotropicdistillation in the reaction of a dimethyl carbonate with phenol [seeUnexamined Japanese Patent Application Laid-Open Specification No.54-48732 (corresponding to West German Patent Application PublicationNo. 2736063 and U.S. Pat. No. 4,252,737) and Unexamined Japanese PatentApplication Laid-Open Specification No. 61-291545], and a method inwhich by-produced methanol is removed by adsorbing the same onto amolecular sieve [Unexamined Japanese Patent Application Laid-OpenSpecification No. 58-185536 (corresponding to U.S. Pat. No. 4,410,464and West German Patent Application Publication No. 3308921)].

Further, a method is known in which an apparatus comprising a reactorhaving provided on the top thereof a distillation column is employed inorder to separate and distill off alcohols (by-produced in the course ofthe reaction) from a reaction mixture obtained in the reactor. [Withrespect to this method, reference can be made to, for example,Unexamined Japanese Patent Application Laid-Open Specification No.56-123948 (corresponding to U.S. Pat. No. 4,182,726 and West GermanPatent Application Publication No. 2528412), Unexamined Japanese PatentApplication Laid-Open Specification No. 56-25138, Unexamined JapanesePatent Application Laid-Open Specification No. 60-169444 (correspondingto U.S. Pat. No. 4,554,110 and West German Patent ApplicationPublication No. 3445552), Unexamined Japanese Patent ApplicationLaid-Open Specification No. 60-169445 (corresponding to U.S. Pat. No.4,552,704 and West German Patent Application Publication No. 3445555),Unexamined Japanese Patent Application Laid-Open Specification No.60-173016 (corresponding to U.S. Pat. No. 4,609,501 and West GermanPatent Application Publication No. 3445553), Unexamined Japanese PatentApplication Laid-Open Specification No. 61-172852, Unexamined JapanesePatent Application Laid-Open Specification No. 61-291545, and UnexaminedJapanese Patent Application Laid-Open Specification No. 62-277345.]

As more preferred methods for producing an aromatic carbonate, thepresent inventors previously developed a method in which a dialkylcarbonate and an aromatic hydroxy compound are continuously fed to acontinuous multi-stage distillation column to effect a continuoustransesterification reaction in the distillation column, whilecontinuously withdrawing a low boiling point reaction mixture containinga by-produced alcohol from an upper portion of the distillation columnby distillation and continuously withdrawing a high boiling pointreaction mixture containing a produced alkyl aryl carbonate from a lowerportion of the distillation column [see Unexamined Japanese PatentApplication Laid-Open Specification No. 3-291257 (corresponding to U.S.Pat. No. 5,210,268 and European Patent Publication No. 0 461 274)], anda method in which an alkyl aryl carbonate is continuously fed to acontinuous multi-stage distillation column to effect a continuoustransesterification reaction in the distillation column, whilecontinuously withdrawing a low boiling point reaction mixture containinga by-produced dialkyl carbonate by distillation and continuouslywithdrawing a high boiling point reaction mixture containing a produceddiaryl carbonate from a lower portion of the distillation column [seeUnexamined Japanese Patent Application Laid-Open Specification No.4-9358 (corresponding to U.S. Pat. No. 5,210,268 and European PatentPublication No. 0 461 274)]. These methods for the first time realizedefficient, continuous production of an aromatic carbonate. Thereafter,various methods for continuously producing an aromatic carbonate havefurther been developed, based on the above-mentioned methods developedby the present inventors. Examples of these methods include a method inwhich a catalytic transesterification reaction is performed in a columnreactor [see Unexamined Japanese Patent Application Laid-OpenSpecification No. 6-41022 (corresponding to U.S. Pat. No. 5,362,901 andEuropean Patent Publication No. 0 572 870), Unexamined Japanese PatentApplication Laid-Open Specification No. 6-157424 (corresponding to U.S.Pat. No. 5,334,724 and European Patent Publication No. 0 582 931),Unexamined Japanese Patent Application Laid-Open Specification No.6-184058 (corresponding to U.S. Pat. No. 5,344,954 and European PatentPublication No. 0 582 930)], a method in which use is made of aplurality of reactors which are connected in series [Unexamined JapanesePatent Application Laid-Open Specification No. 6-234707 (correspondingto U.S. Pat. No. 5,463,102 and European Patent Publication No. 0 608 710A1), and Unexamined Japanese Patent Application Laid-Open SpecificationNo. 6-263694], a method in which a bubble tower reactor is used[Unexamined Japanese Patent Application Laid-Open Specification No.6-298700 (corresponding to U.S. Pat. No. 5,523,451 and European PatentPublication No. 0 614 877)], and a method in which a vertically longreactor vessel is used (Unexamined Japanese Patent Application Laid-OpenSpecification No. 6-345697).

Also, there have been proposed methods for producing an aromaticcarbonate stably for a prolonged period of time on a commercial scale.For example, Unexamined Japanese Patent Application Laid-OpenSpecification No. 6-157410 (corresponding to U.S. Pat. No. 5,380,908 andEuropean Patent Publication No. 0 591 923 A1) discloses a method forproducing aromatic carbonates from a dialkyl carbonate and an aromatichydroxy compound, which comprises continuously supplying a mixture ofraw materials and a catalyst to a reactor provided with a distillationcolumn thereon to effect a transesterification reaction in the reactor,while continuously withdrawing a by-produced aliphatic alcohol from thereactor through the distillation column by distillation so as to keepthe aliphatic alcohol concentration of the reaction system at 2% byweight or less. This prior art document describes that, by this method,continuous production of an aromatic carbonate can be performed in astable manner. The object of this method is to avoid the deposition ofthe catalyst in the distillation column. Further, Patent Applicationprior-to-examination Publication (Kohyo) No. 9-11049 (corresponding toWO 97/11049) discloses a process for producing an aromatic carbonate, inwhich the transesterification is conducted while maintaining a weightratio of an aromatic polyhydroxy compound and/or a residue thereof tothe metal component of the metal-containing catalyst at 2.0 or less,with respect to a catalyst-containing liquid-phase mixture in a systemfor the transesterification, so that the desired aromatic carbonates canbe produced stably for a prolonged period of time without sufferingdisadvantageous phenomena, such as the deposition of the catalyst.

On the other hand, it is known that when an aromatic carbonate isproduced by transesterification, high boiling point substances arelikely to be by-produced. For example, Unexamined Japanese PatentApplication Laid-Open Specification No. 61-172852 discloses that whendiphenyl carbonate is produced by a transesterification of dimethylcarbonate with phenol, an impurity having a boiling point equal to orhigher than the boiling point of the produced diphenyl carbonate isby-produced, and that the impurity is caused to enter the diphenylcarbonate and causes the discoloration of an ultimate product, such asan aromatic polycarbonate. This prior art document does not dis-close anexample of the impurity having a boiling point equal to or higher thanthe boiling point of the produced diphenyl carbonate; however, as anexample of the impurity, there can be mentioned anaryloxycarbonyl-(hydroxy)-arene which is produced as an isomer of adiaryl carbonate by Fries rearrangement. More specifically, whendiphenyl carbonate is produced as the diaryl carbonate, a phenylsalicylate can be mentioned as an example of thearyloxycarbonyl-(hydroxy)-arene. Phenyl salicylate is a high boilingpoint substance whose boiling point is 4 to 5° C. higher than theboiling point of the diphenyl carbonate.

In this case, when the transesterification is conducted for a longperiod of time, the above-mentioned high boiling point substanceaccumulates in the reaction system and the amount of the impurity mixedinto the ultimate aromatic carbonate tends to increase, so that thepurity of the ultimate aromatic carbonate is lowered. Further, as theamount of the high boiling point substance in the reaction mixtureincreases, the boiling point of the reaction mixture rises, so that theby-production of the high boiling point substance is accelerated, thusrendering it difficult to produce desired aromatic carbonates stably fora prolonged period of time. As a measure for solving the problems, it isconceivable to withdraw a high boiling point substance-containingreaction mixture from the reaction system, thereby preventing theaccumulation of the high boiling point substance in the reaction system.However, by this measure, a disadvantage is brought about in that, whena catalyst which is soluble in the reaction liquid is used, both thecatalyst and the high boiling point substance are present in a statedissolved in the reaction mixture, so that, for separating the catalystfrom the high boiling point substance by a conventional distillationmethod, it is necessary to heat the reaction mixture at hightemperatures, leading to a further increased formation of by-products.Therefore, it is difficult to separate the catalyst from the highboiling point substance. This means that the withdrawal of the highboiling point substance from the reaction system is inevitablyaccompanied by the discharge of the catalyst. Accordingly, forcontinuing the reaction, it is necessary to supply a fresh catalyst tothe reaction system. As a result, a large quantity of the catalyst isneeded.

SUMMARY OF THE INVENTION

In this situation, for solving the above-mentioned problems accompanyingthe prior art, the present inventors have made extensive and intensivestudies. As a result, it has been found that:

in a process for producing aromatic carbonates which comprisestransesterifying, in the presence of a metal-containing catalyst, astarting material selected from the group consisting of a dialkylcarbonate, an alkyl aryl carbonate and a mixture thereof with a reactantselected from the group consisting of an aromatic monohydroxy compound,an alkyl aryl carbonate and a mixture thereof,

when use is made of a process characterized in that:

at least one type of catalyst-containing liquid is taken out,

the catalyst-containing liquid being selected from the group consistingof a portion of a high boiling point reaction mixture obtained by theabove transesterification and containing the desired aromatic carbonateand a metal-containing catalyst, and a portion of a liquid catalystfraction obtained by separating the desired aromatic carbonate from thehigh boiling point reaction mixture, wherein each portion containinghigh boiling point substance (A) having a boiling point higher than theboiling point of the produced aromatic carbonate and containing themetal-containing catalyst (B);

a functional substance (C) capable of reacting with at least onecomponent selected from the group consisting of the high boiling pointsubstance (A) and the metal-containing catalyst (B) is added to thetaken-out catalyst-containing liquid, to thereby obtain at least onereaction product selected from the group consisting of an reactionproduct (A)/(C) and a reaction product (B)/(C); and

the reaction product (B)/(C) is recycled to the reaction system directlyor indirectly, while withdrawing the high boiling point substancewithout withdrawing the catalyst from the reaction system,

disadvantageous phenomena, such as the accumulation of the high boilingpoint substance (A) in the reaction system which causes thediscoloration of an ultimate aromatic polycarbonate (which is producedfrom an aromatic carbonate), can be prevented, so that a high purityaromatic carbonate can be stably produced for a prolonged period oftime. The present invention has been completed, based on the abovefinding.

Accordingly, it is a primary object of the present invention to providean improved process for producing an aromatic carbonate, which comprisestransesterifying, in the presence of a metal-containing catalyst, astarting material selected from the group consisting of a dialkylcarbonate, an alkyl aryl carbonate and a mixture thereof with a reactantselected from the group consisting of an aromatic monohydroxy compound,an alkyl aryl carbonate and a mixture thereof, wherein the desired highpurity aromatic carbonates can be produced stably for a prolonged periodof time without suffering above-mentioned disadvantageous phenomena.

That is, according to the process of the present invention, the highboiling point substance can be selectively discharged from the reactionsystem, so that the concentration of the high boiling point substance inthe reaction system can be maintained at a level below a certain valueand hence aromatic carbonates having high purity can be produced.Further, since the catalyst can be recycled, not only can the necessaryamount of the catalyst be remarkably reduced, but also the occurrence ofa catalyst-containing waste containing a high boiling point substance,which used to occur in the conventional technique for the withdrawal ofa high boiling point substance out of the reaction system, can beprevented.

The foregoing and other objects, features and advantages of the presentinvention will be apparent from the following detailed description andappended claims taken in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 is a diagram showing an example of systems for practicing theprocess of the present invention;

FIG. 2 is a diagram showing another example of systems for practicingthe process of the present invention;

FIG. 3 is a diagram showing a further example of systems for practicingthe process of the present invention; and

FIG. 4 is a diagram showing still a further example of systems forpracticing the process of the present invention.

FIG. 5 is a diagram showing still a further example of systems forpracticing the process of the present invention.

DESCRIPTION OF REFERENCE NUMERALS

1, 101, 201: continuous multi-stage distillation column

2, 102, 202: top of the continuous multi-stage distillation column

3, 5, 7, 9, 10, 12, 13, 15, 15′, 16, 18, 19, 20, 20′, 21, 23, 25, 27,28, 29, 30, 32, 34, 35, 37, 39, 40, 41, 44, 45, 46, 48, 48′, 49, 51, 53,55A, 56, 59A, 58, 60, 61, 63, 105, 113, 115, 115′, 116, 118, 119, 120,121, 124, 125, 127, 128, 129, 130, 132, 149, 224, 225, 227, 228, 229,230, 232, 233, 235: conduit

4: preheater

6, 106, 206: bottom of the continuous multi-stage distillation column

8: evaporator

11, 22, 26, 127, 226, 234: condenser

14, 114: evaporator

17, 31, 117, 131: reboiler

24, 43, 54, 62: distillation column

33: thin-film evaporator

36, 47, 59: storage vessel

38: electric furnace

42, 50, 55, 100: reaction vessel

DETAILED DESCRIPTION OF THE INVENTION

In the present invention, there is provided a process for producingaromatic carbonates, which comprises:

(1) transesterifying a starting material selected from the groupconsisting of a dialkyl carbonate represented by the formula (1)

an alkyl aryl carbonate represented by the formula (2)

and a mixture thereof with a reactant selected from the group consistingof an aromatic monohydroxy compound represented by the formula (3)

Ar¹OH  (3),

an alkyl aryl carbonate represented by the formula (4)

and a mixture thereof,

wherein each of R¹, R² and R³ independently represents an alkyl grouphaving 1 to 10 carbon atoms, an alicyclic group having 3 to 10 carbonatoms or an aralkyl group having 6 to 10 carbon atoms, and each of Ar¹,Ar² and Ar³ independently represents an aromatic group having 5 to 30carbon atoms,

in the presence of a metal-containing catalyst which is soluble in areaction system comprising the starting material and the reactant andwhich is present in a state dissolved in the reaction system, to therebyobtain a high boiling point reaction mixture comprising themetal-containing catalyst and at least one aromatic carbonate which isproduced by the transesterification and which corresponds to thestarting material and the reactant and is selected from the groupconsisting of an alkyl aryl carbonate represented by the formula (5)

and a diaryl carbonate represented by the formula (6)

wherein R and Ar are, respectively, selected from the group consistingof R¹, R² and R³ and selected from the group consisting of Ar¹, Ar² andAr³ in correspondence to the starting material and the reactant,

while withdrawing a low boiling point reaction mixture which contains alow boiling point by-product comprising an aliphatic alcohol, a dialkylcarbonate or a mixture thereof corresponding to the starting materialand the reactant and represented by at least one formula selected fromthe group consisting of ROH and

wherein R is as defined above,

(2) separating the high boiling point reaction mixture into a productfraction comprising the produced aromatic carbonate and a liquidcatalyst fraction comprising the metal-containing catalyst, and

(3) recycling the liquid catalyst fraction to the reaction system whilewithdrawing the product fraction,

characterized in that the process further comprises:

(1′) taking out at least one type of catalyst-containing liquid which isselected from the group consisting of:

a portion of the high boiling point reaction mixture before theseparation of the high boiling point reaction mixture into the productfraction and the liquid catalyst fraction, and

a portion of the separated liquid catalyst fraction,

each portion containing (A) at least one high boiling point substancehaving a boiling point higher than the boiling point of the producedaromatic carbonate and containing (B) the metal-containing catalyst,

(2′) adding to the taken-out catalyst-containing liquid a functionalsubstance (C) capable of reacting with at least one component selectedfrom the group consisting of the component (A) and the component (B), tothereby obtain at least one reaction product selected from the groupconsisting of an (A)/(C) reaction product and a (B)/(C) reactionproduct, and

(3′) recycling the (B)/(C) reaction product to the reaction systemdirectly or indirectly, while withdrawing the (A)/(C) reaction product.

For an easy understanding of the present invention, the essentialfeatures and various preferred embodiments of the present invention areenumerated below.

1. A process for producing aromatic carbonates, which comprises:

(1) transesterifying a starting material selected from the groupconsisting of a dialkyl carbonate represented by the formula (1)

an alkyl aryl carbonate represented by the formula (2)

and a mixture thereof with a reactant selected from the group consistingof an aromatic monohydroxy compound represented by the formula (3)

Ar¹OH  (3),

an alkyl aryl carbonate represented by the formula (4)

and a mixture thereof,

wherein each of R¹, R² and R³ independently represents an alkyl grouphaving 1 to 10 carbon atoms, an alicyclic group having 3 to 10 carbonatoms or an aralkyl group having 6 to 10 carbon atoms, and each of Ar¹,Ar² and Ar³ independently represents an aromatic group having 5 to 30carbon atoms,

in the presence of a metal-containing catalyst which is soluble in areaction system comprising the starting material and the reactant andwhich is present in a state dissolved in the reaction system, to therebyobtain a high boiling point reaction mixture comprising themetal-containing catalyst and at least one aromatic carbonate which isproduced by the transesterification and which corresponds to thestarting material and the reactant and is selected from the groupconsisting of an alkyl aryl carbonate represented by the formula (5)

and a diaryl carbonate represented by the formula (6)

wherein R and Ar are, respectively, selected from the group consistingof R¹, R² and R³ and selected from the group consisting of Ar¹, Ar² andAr³ in correspondence to the starting material and the reactant,

while withdrawing a low boiling point reaction mixture which contains alow boiling point by-product comprising an aliphatic alcohol, a dialkylcarbonate or a mixture thereof corresponding to the starting materialand the reactant and represented by at least one formula selected fromthe group consisting of ROH and

wherein R is as defined above,

(2) separating the high boiling point reaction mixture into a productfraction comprising the produced aromatic carbonate and a liquidcatalyst fraction comprising the metal-containing catalyst, and

(3) recycling the liquid catalyst fraction to the reaction system whilewithdrawing the product fraction,

characterized in that the process further comprises:

(1′) taking out at least one type of catalyst-containing liquid which isselected from the group consisting of:

a portion of the high boiling point reaction mixture before theseparation of the high boiling point reaction mixture into the productfraction and the liquid catalyst fraction, and

a portion of the separated liquid catalyst fraction,

each portion containing (A) at least one high boiling point substancehaving a boiling point higher than the boiling point of the producedaromatic carbonate and containing (B) the metal-containing catalyst,

(2′) adding to the taken-out catalyst-containing liquid a functionalsubstance (C) capable of reacting with at least one component selectedfrom the group consisting of the component (A) and the component (B), tothereby obtain at least one reaction product selected from the groupconsisting of an (A)/(C) reaction product and a (B)/(C) reactionproduct, and

(3′) recycling the (B)/(C) reaction product to the reaction systemdirectly or indirectly, while withdrawing the (A)/(C) reaction product.

2. The process according to item 1 above, wherein the portion of thehigh boiling point reaction mixture is from 0.01 to 10% by weight, basedon the weight of the high boiling point reaction mixture, and whereinthe portion of the separated liquid catalyst fraction is from 0.01 to40% by weight, based on the weight of the separated liquid catalystfraction.

3. The process according to item 1 or 2 above, wherein the high boilingpoint substance (A) originates from at least one compound selected fromthe group consisting of the starting material, the reactant, impuritiescontained in the starting material and the reactant, and by-products ofthe transesterification reaction.

4. The process according to item 3 above, wherein the high boiling pointsubstance (A) is at least one substance selected from the groupconsisting of an aromatic hydroxy compound (7), a compound (8) derivedfrom the compound (7), an aromatic carboxy compound (9), a compound (10)derived from the compound (9), and xanthone,

wherein:

compound (7) is represented by the formula (7):

 wherein Ar⁴ represents an aromatic group having a valence of m, mrepresents an integer of 2 or more, and each —OH group is independentlybonded to an arbitrary ring-carbon position of the Ar⁴ group,

compound (8) contains a residue represented by the formula (8):

 wherein Ar⁴ and m are as defined for formula (7), n represents aninteger of from 1 to m, and each of the —OH group and the —O— group isindependently bonded to an arbitrary ring-carbon position of the Ar⁴group,

compound (9) is represented by the formula (9):

 wherein Ar⁵ represents an aromatic group having a valence of r, rrepresents an integer of 1 or more, s represents an integer of from 0 to(r−1), and each of the —OH group and the —COOH group is independentlybonded to an arbitrary ring-carbon position of the Ar⁵ group, and

compound (10) contains a residue represented by the formula (10):

 wherein Ar⁵, r and s are as defined for formula (9), t is an integer offrom 0 to s, u is an integer of from 0 to (r−s), with the proviso that tand u are not simultaneously 0, and each of the —OH group, the —COOHgroup, the —O— group and the —(COO)— group is independently bonded to anarbitrary ring-carbon position of the Ar⁵ group.

5. The process according to any one of items 1 to 4 above, wherein thefunctional substance (C) is an oxidizing agent, so that the (A)/(C)reaction product is a low boiling point oxidation product and the(B)/(C) reaction product is a metal oxide.

6. The process according to any one of items 1 to 4 above, wherein thefunctional substance (C) is a precipitant, so that the (B)/(C) reactionproduct is a metal-containing substance which precipitates.

7. The process according to item 6 above, wherein the metal-containingsubstance is a metal compound selected from the group consisting of ametal carbonate, a metal hydroxide, a metal oxide, a metal sulfide and ametal sulfate.

8. The process according to any one of items 1 to 4 above, wherein thefunctional substance (C) is a reactive solvent, so that the (A)/(C)reaction product is a low boiling point product obtained by thesolvolysis of component (A).

9. The process according to item 8 above, wherein the reactive solventis water, so that the (A)/(C) reaction product is an aromaticmonohydroxy compound obtained by the hydrolysis of component (A).

10. The process according to any one of items 1 to 9 above, wherein thesteps (1), (2) and (3) are continuously performed, thereby continuouslyproducing an aromatic carbonate.

11. The process according to item 10 above, wherein the startingmaterial and the reactant are continuously fed to a continuousmulti-stage distillation column to effect a transesterification reactiontherebetween in at least one phase selected from the group consisting ofa liquid phase and a gas-liquid phase in the presence of themetal-containing catalyst in the distillation column, while continuouslywithdrawing a high boiling point reaction mixture containing theproduced aromatic carbonate in a liquid form from a lower portion of thedistillation column and continuously withdrawing a low boiling pointreaction mixture containing the low boiling point by-product in agaseous form from an upper portion of the distillation column bydistillation.

12. A process for producing aromatic polycarbonates, which comprisessubjecting to transesterification polymerization an aromatic carbonateproduced by the process according to any one of items 1 to 11 above andan aromatic dihydroxy compound.

The process of the present invention for producing an aromatic carbonatefrom the above-mentioned starting material and reactant bytransesterification in the presence of a metal-containing catalyst ischaracterizd in that:

at least one type of catalyst-containing liquid is taken out,

the catalyst-containing liquid being selected from the group consistingof:

a portion of a high boiling point reaction mixture obtained by the abovetransesterification and containing the desired aromatic carbonate and ametal-containing catalyst, and

a portion of a liquid catalyst fraction obtained by separating thedesired aromatic carbonate from the high boiling point reaction mixture,

each portion containing high boiling point substance (A) having aboiling point higher than the boiling point of the produced aromaticcarbonate and containing the metal-containing catalyst (B);

a functional substance (C) capable of reacting with at least onecomponent selected from the group consisting of the high boiling pointsubstance (A) and the metal-containing catalyst (B) is added to thetaken-out catalyst-containing liquid, to thereby obtain at least onereaction product selected from the group consisting of an (A)/(C)reaction product and a (B)/(C) reaction product; and

the (B)/(C) reaction product is recycled to the reaction system, whilewithdrawing the (A)/(C) reaction product.

As described above, when the metal-containing catalyst soluble in thereaction system is used, the separation of the high boiling pointreaction mixture into the catalyst (B) and the high boiling pointsubstance (A) by the conventional techniques is difficult.

Therefore, the recycling of only the catalyst (B) to the reaction systemwas conventionally impossible.

In the process of the present invention, by reacting thecatalyst-containing liquid containing a high boiling point substance (A)and a metal-containing catalyst (B) with a functional substance (C), an(A)/(C) reaction product and/or a (B)/(C) reaction product can beobtained. The separation between the (A)/(C) reaction product and the(B)/(C) reaction product can be easily performed. Thus, it has for thefirst time been possible to withdraw the high boiling point substance(A) out of the reaction system, while recycling the catalyst (B) to thereaction system.

The present invention is described below in detail.

The dialkyl carbonate used as a starting material in the presentinvention is represented by formula (1):

wherein R¹ represents an alkyl group having 1 to 10 carbon atoms, analicyclic group having 3 to 10 carbon atoms or an aralkyl group having 6to 10 carbon atoms. Examples of R¹ include an alkyl group, such asmethyl, ethyl, propyl (isomers), allyl, butyl (isomers), butenyl(isomers), pentyl (isomers), hexyl (isomers), heptyl (isomers), octyl(isomers), nonyl (isomers), decyl (isomers) and cyclohexylmethyl; analicyclic group, such as cyclopropyl, cyclobutyl, cyclopentyl,cyclohexyl and cycloheptyl; and an aralkyl group, such as benzyl,phenethyl (isomers), phenylpropyl (isomers), phenylbutyl (isomers) andmethylbenzyl (isomers). The above-mentioned alkyl group, alicyclic groupand aralkyl group may be substituted with a substituent, such as a loweralkyl group, a lower alkoxy group, a cyano group and a halogen atom, aslong as the number of carbon atoms of the substituted group does notexceed 10, and may also contain an unsaturated bond.

As a dialkyl carbonate having such R¹, there may be mentioned forexample, dimethyl carbonate, diethyl carbonate, dipropyl carbonate(isomers), diallyl carbonate, dibutenyl carbonate (isomers), dibutylcarbonate (isomers), dipentyl carbonate (isomers), dihexyl carbonate(isomers), diheptyl carbonate (isomers), dioctyl carbonate (isomers),dinonyl carbonate (isomers), didecyl carbonate (isomers), dicyclopentylcarbonate, dicyclohexyl carbonate, dicycloheptyl carbonate, dibenzylcarbonate, diphenethyl carbonate (isomers), di(phenylpropyl) carbonate(isomers), di(phenylbutyl) carbonate (isomers), di(chlorobenzyl)carbonate (isomers), di(methoxybenzyl) carbonate (isomers),di(methoxymethyl) carbonate, di(methoxyethyl) carbonate (isomers),di(chloroethyl) carbonate (isomers) and di(cyanoethyl) carbonate(isomers). These dialkyl carbonates can also be used in mixture.

Of these dialkyl carbonates, a dialkyl carbonate containing as R¹ alower alkyl group having 4 or less carbon atoms is preferably used. Mostpreferred is dimethyl carbonate.

The alkyl aryl carbonate used as the starting material in the presentinvention is represented by the following formula (2):

wherein R² may be identical with or different from R¹, and represents analkyl group having 1 to 10 carbon atoms, an alicyclic group having 3 to10 carbon atoms or an aralkyl group having 6 to 10 carbon atoms; and Ar²represents an aromatic group having 5 to 30 carbon atoms. As R², theremay be mentioned, for example, the same groups as set forth above forR¹.

Illustrative examples of Ar² in formula (2) include:

a phenyl group and various alkylphenyl groups, such as phenyl, tolyl(isomers), xylyl (isomers), trimethylphenyl (isomers), tetramethylphenyl(isomers), ethylphenyl (isomers), propylphenyl (isomers), butylphenyl(isomers), diethylphenyl (isomers), methylethylphenyl (isomers,),pentylphenyl (isomers), hexylphenyl (isomers) and cyclohexylphenyl(isomers);

various alkoxyphenyl groups, such as methoxyphenyl (isomers),ethoxyphenyl (isomers) and butoxyphenyl (isomers);

various halogenated phenyl groups, such as fluorophenyl (isomers),chlorophenyl (isomers), bromophenyl (isomers), chloromethylphenyl(isomers) and dichlorophenyl (isomers);

various substituted phenyl groups represented by the formula (11):

wherein A represents a single bond, a divalent group, such as —O—, —S—,—CO— or —SO₂—, an alkylene group, a substituted alkylene group of thefollowing formula:

wherein each of R⁴, R⁵, R⁶ and R⁷ independently represents a hydrogenatom; or a lower alkyl group, a cycloalkyl group, an aryl group or anaralkyl group, which may be substituted with a halogen atom or an alkoxygroup,

or a cycloalkylene group of the following formula:

wherein k is an integer of from 3 to 11, and the hydrogen atoms may bereplaced by a lower alkyl group, an aryl group, a halogen atom or thelike, and the aromatic ring in formula (2) may be substituted with asubstituent, such as a lower alkyl group, a lower alkoxy group, an estergroup, a hydroxyl group, a nitro group, a halogen atom and a cyanogroup;

a naphthyl group and various substituted naphthyl groups, such asnaphthyl (isomers), methylnaphthyl (isomers), dimethylnaphthyl(isomers), chloronaphthyl (isomers), methoxynaphthyl (isomers) andcyanonaphthyl (isomers); and

various unsubstituted or substituted heteroaromatic groups, such aspyridyl (isomers), cumaryl (isomers), quinolyl (isomers), methylpyridyl(isomers), chloropyridyl (isomers), methylcumaryl (isomers) andmethylquinolyl (isomers).

Representative examples of alkyl aryl carbonate having these R² and Ar²include methyl phenyl carbonate, ethyl phenyl carbonate, propyl phenylcarbonate (isomers), allyl phenyl carbonate, butyl phenyl carbonate(isomers), pentyl phenyl carbonate (isomers), hexyl phenyl carbonate(isomers), heptyl phenyl carbonate (isomers), octyl tolyl carbonate(isomers), nonyl ethylphenyl carbonate (isomers), decyl butylphenylcarbonate (isomers), methyl tolyl carbonate (isomers), ethyl tolylcarbonate (isomers), propyl tolyl carbonate (isomers), butyl tolylcarbonate (isomers), allyl tolyl carbonate (isomers), methyl xylylcarbonate (isomers), methyl trimethylphenyl carbonate (isomers), methylchlorophenyl carbonate (isomers), methyl nitrophenyl carbonate(isomers), methyl methoxyphenyl carbonate (isomers), methyl cumylcarbonate (isomers), methyl naphthyl carbonate (isomers), methyl pyridylcarbonate (isomers), ethyl cumyl carbonate (isomers), methylbenzoylphenyl carbonate (isomers), ethyl xylyl carbonate (isomers),benzyl xylyl carbonate (isomers). These alkyl aryl carbonates can alsobe used in mixture. Of these alkyl aryl carbonates, one containing as R²an alkyl group having 1 to 4 carbon atoms and as Ar² an aromatic grouphaving 6 to 10 carbon atoms is preferably used, and methyl phenylcarbonate is most preferred.

The starting material used in the present invention is selected from thegroup consisting of a dialkyl carbonate represented by formula (1)above, an alkya aryl carbonate represented by formula (2) above and amixture thereof.

The aromatic monohydroxy compound used as the reactant in the presentinvention is represented by formula (3):

Ar¹OH  (3)

wherein Ar¹ may be identical with or different from Ar², represents anaromatic group having 5 to 30 carbon atoms, and the type of the compoundis not limited as long as the hydroxyl group is directly bonded to thearomatic group. As Ar¹, there may be mentioned, for example, the samegroups as set forth above for Ar².

Preferred examples of aromatic monohydroxy compounds of formula (3)include phenol; various alkylphenols, such as cresol (isomers), xylenol(isomers), trimethylphenol (isomers), tetramethylphenol (isomers),ethylphenol (isomers), propylphenol (isomers), butylphenol (isomers),diethylphenol (isomers), methylethylphenol (isomers), methylpropylphenol(isomers), dipropylphenol (isomers), methylbutylphenol (isomers),pentylphenol (isomers), hexylphenol (isomers) and cyclohexylphenol(isomers); various alkoxyphenols, such as methoxyphenol (isomers) andethoxyphenol (isomers); various substituted phenols represented by thefollowing formula (12):

wherein A is as defined above; naphthol (isomers) and varioussubstituted naphthols; and heteroaromatic monohydroxy compounds, such ashydroxypyridine (isomers), hydroxycumarine (isomers) andhydroxyquinoline (isomers). These aromatic monohydroxy compounds canalso be used in mixture.

Of these aromatic monohydroxy compounds, an aromatic monohydroxycompound containing as Ar¹ an aromatic group having 6 to 10 carbon atomsis preferably used in the present invention, and phenol is mostpreferred.

The alkyl aryl carbonate used as the reactant in the present inventionis represented by the following formula (4):

wherein R³ may be identical with or different from R¹ and R² ₇ andrepresents an alkyl group having 1 to 10 carbon atoms, as alicyclicgroup having 3 to 10 carbon atoms or an aralkyl group having 6 to 10carbon atoms; and Ar³ may be identical with or different from Ar¹ andAr², and represents an aromatic group having 5 to 30 carbon atoms. AsR³, there may be mentioned, for example, the same groups as set forthabove for R¹. As Ar³, there may be mentioned, for example, the samegroups as set forth above for Ar².

As alkyl aryl carbonates having these R³ and Ar³, there may be mentionedfor example, those which are set forth above for alkyl aryl carbonatesrepresented by the above-mentioned formula (2).

Of these alkyl aryl carbonates, one containing as R³ an alkyl grouphaving 1 to 4 carbon atoms and as Ar³ an aromatic group having 6 to 10carbon atoms is preferably used, and methyl phenyl carbonate is mostpreferred.

The reactant used in the present invention is selected from the groupconsisting of a aromatic monohydroxy compound represented by formula (3)above, an alkyl aryl carbonate represented by formula (4) above and amixture thereof.

The typical reactions, which are involved in the process of the presentinvention for producing an aromatic carbonate or an aromatic carbonatemixture by transesterifying a starting material with a reactant in thepresence of a metal-containing catalyst, are represented by thefollowing formulae (E1), (E2), (E3) and (E4):

wherein R¹, R², R³, Ar¹, Ar² and Ar³ are as defined above, each of Ar'sappearing in formula (E4) independently represents Ar² or Ar³, and eachof R's appearing in formula (E4) independently represents R² or R³, andwherein when R²═R³ and Ar²═Ar³ in formula (E4), the reaction is asame-species intermolecular transesterification reaction generally knownas a disproportionation reaction.

When each of the reactions of formulae (E1), (E2), (E3) and (E4) isperformed according to the process of the present invention, dialkylcarbonates or alkyl aryl carbonates as the starting materials for thereaction can be used individually or in mixture and aromatic monohydroxycompounds or alkyl aryl carbonates as the reactants for the reaction canbe used individually or in mixture.

When R²═R³═R and Ar²═Ar³═Ar in the transesterification reaction offormula (E4), a diaryl carbonate and a dialkyl carbonate can be obtainedby a same-species intermolecular transesterification reaction of asingle type of alkyl aryl carbonate. This is a preferred embodiment ofthe present invention.

Further, when R¹═R²═R³═R and Ar¹═Ar²═Ar³═Ar in formulae (E1) and (E4),by combining the reaction of formula (E1) with the reaction of formula(E4), a diaryl carbonate can be obtained from a dialkyl carbonate and anaromatic monohydroxy compound through an alkyl aryl carbonate as shownin formulae (E5) and (E6). This is an especially preferred embodiment ofthe present invention.

Recycling of the dialkyl carbonate by-produced in the reaction offormula (E6) as the starting material for the reaction of formula (E5)results in the formation of 1 mol of a diaryl carbonate and 2 mol of analiphatic alcohol from 1 mol of a dialkyl carbonate and 2 mol of anaromatic monohydroxy compound.

When R═CH₃ and Ar═C₆H₅ in the above formulae (E5) and (E6), diphenylcarbonate, which is an important raw material for a polycarbonate and anisocyanate, can be readily obtained from dimethyl carbonate, which isthe simplest form of a dialkyl carbonate, and phenol. This is especiallyimportant.

The metal-containing catalyst used in the present invention is onecapable of promoting the reactions of formulae (E1) to (E4). As suchmetal-containing catalysts, there may be mentioned for example:

<lead compounds>

lead oxides, such as PbO, PbO₂ and Pb₃O₄; lead sulfides, such as PbS andPb₂S; lead hydroxides, such as Pb(OH)₂ and Pb₂O₂(OH)₂; plumbites, suchas Na₂PbO₂, K₂PbO₂, NaHPbO₂ and KHPbO₂; plumbates, such as Na₂PbO₃,Na₂H₂PbO₄, K₂PbO₃, K₂[Pb(OH)₆], K₄PbO₄, Ca₂PbO₄ and CaPbO₃; leadcarbonates and basic salts thereof, such as PbCO₃ and 2PbCO3.Pb(OH)₂;lead salts of organic acids, and carbonates and basic salts thereof,such as Pb(OCOCH₃)₂, Pb(OCOCH₃)₄ and Pb(OCOCH₃)₂.PbO.3H₂O; organoleadcompounds, such as Bu₄Pb, Ph₄Pb, Bu₃PbC₁, Ph₃PbBr, Ph₃Pb (or Ph₆Pb₂),Bu₃PbOH and Ph₃PbO wherein Bu represents a butyl group and Ph representsa phenyl group; alkoxylead compounds and aryloxylead compounds, such asPb(OCH₃)₂, (CH₃O)Pb(OPh) and Pb(OPh)₂; lead alloys, such as Pb—Na,Pb—Ca, Pb—Ba, Pb—Sn and Pb—Sb; lead minerals, such as galena and zincblende; and hydrates of these lead compounds;

<copper family metal compounds>

salts or complexes of copper family metals, such as CuCl, CuCl₂, CuBr,CuBr₂, CuI, CuI₂, Cu(OAc)₂, Cu(acac)₂, copper oleate, Bu₂Cu, (CH₃O)₂Cu,AgNO₃, AgBr, silver picrate, AgC₆H₆ClO₄, Ag(bullvalene)₃NO₃,[AuC≡C—C(CH₃)₃]_(n) and [Cu(C₇H₈)Cl]₄ wherein Ac represents an acetylgroup and acac represents an acetylacetone chelate ligand;

<alkali metal complexes>

alkali metal complexes, such as Li(acac) and LiN(C₄H₉)₂;

<zinc complexes>

zinc complexes, such as Zn(acac)₂;

<cadmium complexes>

cadmium complexes, such as Cd(acac)₂;

<iron family metal compounds>

iron family metal complexes, such as Fe(C₁₀H₈)(CO)₅, Fe(CO)₅,Fe(C₃H₆)(CO)₃, Co(mesitylene)₂(PEt₂Ph)₂, CoC₅F₅(CO)₂, Ni-π-C₅H₅NO andferrocene;

<zirconium complexes>

zirconium complexes, such as Zr(acac)₄ and zirconocene;

<Lewis acids and Lewis acid-forming compounds>

Lewis acids and Lewis acid-forming transition metal compounds, such asAlX₃, TiX₃, TiX₄, VOX₃, VX₅, ZnX₂, FeX₃ and SnX₄ wherein X represents ahalogen atom, an acetoxy group, an alkoxy group or an aryloxy group; and

<organotin compounds>

organotin compounds, such as (CH₃)₃SnOCOCH₃, (C₂H₅)₃SnOCOC₆H₅,Bu₃SnOCOCH₃, Ph₃SnOCOCH₃, Bu₂Sn(OCOCH₃)₂, Bu₂Sn(OCOC₁₁H₂₃)₂, Ph₃SnOCH₃,(C₂H₅)₃SnOPh, Bu₂Sn(OCH₃)₂, Bu₂Sn(OC₂H₅)₂, Bu₂Sn(OPh)₂, Ph₂Sn(OCH₃)₂,(C₂H₅)₃SnOH, Ph₃SnOH, Bu₂SnO, (C₈H₁₇)₂SnO, Bu₂SnCl₂ and BuSnO(OH)wherein Ph represents an phenyl group.

These catalysts are effective even when they are reacted with an organiccompound present in the reaction system, such as an aliphatic alcohol,an aromatic monohydroxy compound, an alkyl aryl carbonate, a diarylcarbonate and a dialkyl carbonate. Those which are obtained byheat-treating these catalysts together with a starting material, areactant and/or a reaction product thereof prior to the use in theprocess of the present invention can also be used.

It is preferred that the metal-containing catalyst have high solubilityin the liquid phase of the reaction system. Preferred examples ofmetal-containing catalysts include Pb compounds, such as PbO, Pb(OH)₂and Pb(OPh)₂; Ti compounds, such as TiCl₄ and Ti(OPh)₄; Sn compounds,such as SnCl₄, Sn(OPh)₄, Bu₂SnO and Bu₂Sn(OPh)₂; Fe compounds, such asFeCl₃, Fe(OH)₃ and Fe(OPh)₃; and those products which are obtained bytreating the above metal compounds with phenol or a liquid phase of thereaction system.

There is no particular limitation with respect to the type of thereactor to be used in the process of the present invention, and varioustypes of conventional reactors, such as a stirred tank reactor, amulti-stage stirred tank reactor and a multi-stage distillation column,can be used. These types of reactors can be used individually or incombination, and may be used either in a batchwise process or acontinuous process. From the viewpoint of efficiently biasing theequilibrium toward the product system, a multi-stage distillation columnis preferred, and a continuous process using a multi-stage distillationcolumn is especially preferred. There is no particular limitation withrespect to the multi-stage distillation column to be used in the presentinvention as long as it is a distillation column having a theoreticalnumber of stages of distillation of two or more and which can be usedfor performing continuous distillation. Examples of such multi-stagedistillation columns include plate type columns using a tray, such as abubble-cap tray, a sieve tray, a valve tray and a counterflow tray, andpacked type columns packed with various packings, such as a Raschigring, a Lessing ring, a Pall ring, a Berl saddle, an Intalox saddle, aDixon packing, a McMahon packing, a Heli pack, a Sulzer packing andMellapak. In the present invention, any of the columns which aregenerally used as a multi-stage distillation column can be utilized.Further, a mixed type of plate column and packed column comprising botha plate portion and a portion packed with packings, can also bepreferably used.

In one preferred embodiment of the present invention, in which thecontinuous production of an aromatic carbonate is conducted using amulti-stage distillation column, a starting material and a reactant arecontinuously fed to a continuous multi-stage distillation column toeffect a transesterification reaction there-between in at least onephase selected from a liquid phase and a gas-liquid phase in thepresence of a metal-containing catalyst in the distillation column,while continuously withdrawing a high boiling point reaction mixturecontaining a produced aromatic carbonate or aromatic carbonate mixturein liquid form from a lower portion of the distillation column andcontinuously withdrawing a low boiling point reaction mixture containinga by-product in gaseous form from an upper portion of the distillationcolumn by distillation.

The amount of the catalyst used in the present invention variesdepending on the type thereof, the types and weight ratio of thestarting material and the reactant, the reaction conditions, such asreaction temperature and reaction pressure, and the like. Generally, theamount of the catalyst is in the range of from 0.0001 to 30% by weight,based on the total weight of the starting material and the reactant.

The reaction time (or the residence time when the reaction iscontinuously conducted) for the transesterification reaction in thepresent invention is not specifically limited, but it is generally inthe range of from 0.001 to 50 hours, preferably from 0.01 to 10 hours,more preferably from 0.05 to 5 hours.

The reaction temperature varies depending on the types of the startingmaterial and reactant, but is generally in the range of from 50 to 350°C., preferably from 100 to 280° C. The reaction pressure variesdepending on the types of the starting material and reactant and thereaction temperature, and it may be any of a reduced pressure, anatmospheric pressure and a superatmospheric pressure. However, thereaction pressure is generally in the range of from 0.1 to 2.0×10⁷ Pa.

In the present invention, it is not necessary to use a reaction solvent.However, for the purpose of facilitating the reaction operation, anappropriate inert solvent, such as an ether, an aliphatic hydrocarbon,an aromatic hydrocarbon or a halogenated aromatic hydrocarbon, may beused as a reaction solvent.

As mentioned above, the process of the present invention ischaracterized by taking out the catalyst-containing liquid containingthe high boiling point substance (A) and a metal-containing catalyst(B); adding a functional substance (C) capable of reacting with the highboiling point substance (A) and/or the metal-containing catalyst (B) tothe taken-out catalyst-containing liquid, to thereby obtain an (A)/(C)reaction product and/or a (B)/(C) reaction product; and recycling the(B)/(C) reaction product directly or indirectly to the reaction system,while withdrawing the (A)/(C) reaction product.

In the process of the present invention, the passage “recycling the(B)/(C) reaction product directly or indirectly to the reaction system”means “recycling the (B)/(C) reaction product to the reactor directly,or recycling the (B)/(C) reaction product to the reactor indirectlythrough a pipe and a device which communicate with the inlet of thereactor or which are used for recovering the catalyst”.

The “catalyst-containing liquid containing the high boiling pointsubstance and a metal-containing catalyst” means at least one type ofcatalyst-containing liquid which is selected from the group consistingof a portion of the high boiling point reaction mixture before theseparation of the high boiling point reaction mixture into the productfraction and the liquid catalyst fraction, and a portion of theseparated liquid catalyst fraction. More specifically, theabove-mentioned catalyst-containing liquid means, for example, acatalyst-containing liquid which is selected from the group consistingof a portion of the reaction mixture (containing the metal-containingcatalyst (B) and the high boiling point substance (A)) which iswithdrawn from the reactor, or a portion of a liquid material (havingincreased concentrations with respect to the catalyst and the highboiling point substance) which is obtained by subjecting to evaporationa part of the catalyst-containing reaction mixture withdrawn from thereactor. In the catalyst-containing liquid, the catalyst may becompletely dissolved, or may be in the form of a slurry in whichinsoluble matters are formed by the reaction between the catalyst andthe high boiling point substance. In the present invention, when thecatalyst-containing liquid is in the form of a slurry, a portion in theslurry which is present in a non-dissolved state is also included in the“catalyst-containing liquid containing the high boiling point substance(A) and a metal-containing catalyst (B)”. The catalyst-containing liquidmay be taken out continuously or intermittently.

In the process of the present invention, the “high boiling pointsubstance (A)” means a substance having a boiling point higher than theboiling point of the produced aromatic carbonates, wherein such asubstance originates from at least one compound selected from the groupconsisting of the starting material, the reactant, impurities containedin the starting material and the reactant, and by-products of thetransesterification reaction. Examples of such high boiling pointsubstances (A) include an aromatic hydroxy compound, a compoundcontaining a residue of the aromatic hydroxy compound, an aromatic acompound, a compound containing a residue of the aromatic carboxycompound, and xanthone. Those by-products having a high molecular weightwhich are produced, by reaction, from the aromatic hydroxy compound, acompound containing a residue of the aromatic hydroxy compound, anaromatic carboxy compound, a compound containing a residue of thearomatic carboxy compound, and xanthone can also be mentioned asexamples of above-mentioned high boiling point substances (A).

In the present invention, the aromatic hydroxy compound is representedby the following formula (7):

wherein Ar⁴ represents an aromatic group having a valence of m, mrepresents an integer of 2 or more, and each —OH group is individuallybonded to an arbitrary ring-carbon position of the Ar⁴ group.

The residue of the aromatic hydroxy compound is represented by thefollowing formula (8):

wherein Ar⁴ and m are as defined above, n represents an integer of from1 to m, and each of the —OH group and the —O— group is individuallybonded to an arbitrary ring-carbon position of the Ar⁴ group.

The residue (8) of the aromatic hydroxy compound is present in such aform as chemically bonded to at least one member selected from the groupconsisting of the metal of the metal-containing catalyst, analkoxycarbonyl group derived from the dialkyl carbonate or the alkylaryl carbonate, an aryloxycarbonyl group derived from the alkyl arylcarbonate or the diaryl carbonate, and a carbonyl group derived from thedialkyl carbonate, the alkyl aryl carbonate or the diaryl carbonate.

Illustrative examples of the Ar⁴ groups in formulae (7) and (8) aboveinclude aromatic groups represented by the following formulae (13),(14), (15), (16) and (17):

wherein Y¹ represents a single bond, a divalent alkane group having 1 to30 carbon atoms or a divalent group selected from —O—, —CO—, —S—, —SO₂—,—SO— and —COO—,

wherein each of two Y^(1′)s is as defined above, and two Y^(1′)s may bethe same or different;

wherein Z represents a trivalent group, such as a C₁-C₃₀ trivalentalkane group or a trivalent aromatic group; and at least one hydrogenatom of each aromatic ring may be replaced with a substitutent, such asa halogen atom, a C₁-C₃₀ alkyl group, a C₁-C₃₀ alkoxy group, a phenylgroup, a phenoxy group, a vinyl group, a cyano group, an ester group, anamido group, a nitro group or the like; and

Examples of these aromatic polyhydroxy compounds include hydroquinone,resorcin, catechol, trihydroxybenzene (isomers),bis(hydroxyphenyl)propane (isomers), bis(hydroxyphenyl)methane(isomers), bis(hydroxyphenyl)ether (isomers), bis(hydroxyphenyl)ketone(isomers), bis(hydroxyphenyl)sulfone (isomers),bis(hydroxyphenyl)sulfide (isomers), dihydroxy diphenyl (isomers),bis(dihydroxyphenyl)methane (isomers), 2-hydroxyphenyl hydroxypropylphenol, dihydroxy (hydroxyphenyl diphenyl) (isomers),tri-(hydroxyphenyl)ethane (isomers), tri-(hydroxyphenyl)benzene(isomers), dihydroxynaphthalene (isomers) and trihydroxynaphthalene(isomers).

Of these aromatic hydroxy compounds and compounds having a residue ofthe aromatic hydroxy compounds, attention should be made to thosecompounds which are likely to be present in the system for thetransesterification for the production of an aromatic carbonate. As sucha compound, there can be mentioned at least one member selected from thegroup consisting of:

(a) an oxidation product of an aromatic monohydroxy compound as thereactant,

(b) at least one member selected from the group consisting of a productproduced by the Fries rearrangement of a diaryl carbonate obtained bythe transesterification and oxidation products of the product, and

(c) at least one member selected from the group consisting of aromaticdihydroxy compounds derived from phenol as the reactant and representedby the following formula (18):

wherein Y¹ is as defined above, and oxidation products of the aromaticdihydroxy compounds.

As examples of oxidation products (a) of an aromatic monohydroxycompound, compounds represented by the following formulae (19) and (20)can be mentioned.

As examples of products (b) produced by the Fries rearrangement of adiaryl carbonate, compounds represented by the following formulae (21),(22) and (23) can be mentioned.

As examples of oxidation products of the above-mentioned product (b)produced by the Fries rearrangement of a diaryl carbonate andrepresented by formula (21), compounds represented by the followingformulae (24) and (25) can be mentioned. Also, as examples of respectiveoxidation products of the above-mentioned products (b) represented byformulae (22) and (23), compounds represented by the following formulae(26) and (27) can be mentioned.

As an example of aromatic dihydroxy compounds (c) represented by formula(18), a compound represented by the following formula (28) can bementioned.

As examples of oxidation products of the above-mentioned aromaticdihydroxy compounds (c) represented by formula (28), compoundsrepresented by the following formulae (29) and (30) can be mentioned.

wherein Y¹ is as defined above.

The reason why the above-mentioned oxidation product (a) of an aromaticmonohydroxy compound is likely to be present in the system for thetransesterification for the production of an aromatic carbonate, forexample, is that such an oxidation product is formed by the oxidation ofan aromatic monohydroxy compound with a very small amount of oxygenwhich occasionally enters the system for the transesterification, orthat such an oxidation product is occasionally present as a contaminantof an aromatic monohydroxy compound as a raw material and enters thesystem together with the raw material. Representative examples of type(a) oxidation products, namely, oxidation products of aromaticmonohydroxy compounds include dihydroxybenzene (isomers), dihydroxydiphenyl (isomers), and the like.

Product (b) produced by the Fries rearrangement of a diaryl carbonate islikely to be formed as a by-product in the production of the diarylcarbonate. Examples of products (b) include 2,2′-dihydroxybenzophenone,2,4′-dihydroxybenzophenone and 4,4′-dihydroxybenzophenone.

The aromatic dihydroxy compound (c) is a compound which is usually usedas a monomer for the production of an aromatic polycarbonate. Anaromatic polycarbonate can be produced by a transesterification of theabove-mentioned aromatic dihydroxy compound (c) with a diaryl carbonate,wherein an aromatic monohydroxy compound is by-produced. When such aby-produced aromatic monohydroxy compound is used as a raw material inthe process of the present invention, the aromatic dihydroxy compound(c) is likely to be introduced into the system for thetransesterification for the production of an aromatic carbonate.Examples of aromatic dihydroxy compounds (c) include2,2-bis-(4-hydroxyphenyl)propane, and the like.

Further, 2,2-bis-(4-hydroxyphenyl)propane usually contains aromaticpolyhydroxy compounds represented by the following formulae, whichcompounds are also included in the aromatic polyhydroxy compound definedin the present invention.

In the present invention, the aromatic carboxy compound, which is one ofthe high boiling point substances, is represented by the followingformula (9):

wherein Ar⁵ represents an aromatic group having a valence of r, rrepresents an integer of 1 or more, s represents an integer of from 0 tor−1, and each of the —OH group and the —(COOH) group is individuallybonded to an arbitrary ring-carbon position of the Ar⁵ group, and

The residue of the aromatic carboxy compound is represented by thefollowing formula (10):

wherein Ar⁵, r and s are as defined above, t represents an integer offrom 0 to s, u represents an integer of from 0 to r—s, with the provisothat t and u are not simultaneously O, and each of the —OH group, the—(COOH) group, the —O— group and the —(COO)— group is individuallybonded to an arbitrary ring-carbon position of the Ar⁵ group.

The residue of the aromatic carboxy compound, which is represented byformula (10), is present in such a form as chemically bonded to at leastone member selected from the group consisting of a metal of themetal-containing catalyst, an alkoxycarbonyl group derived from thedialkyl carbonate or the alkyl aryl carbonate, an alkyl group formed bythe decarboxylation reaction of the alkoxycarbonyl group, anaryloxycarbonyl group derived from the alkyl aryl carbonate or thediaryl carbonate, an aryl group formed by the decarboxylation reactionof the aryloxycarbonyl group, and a carbonyl group derived from thedialkyl carbonate, the alkyl aryl carbonate or the diaryl carbonate.

Examples of these aromatic carboxy compounds and compounds havingresidues of such aromatic carboxy compounds include aromatic carboxylicacids, such as benzoic acid, terephthalic acid, isophthalic acid andphthalic acid; aromatic carboxylic acid esters, such as methyl benzoate,phenyl benzoate and dimethyl terephthalate; hydroxyaromatic carboxylicacids, such as salicylic acid, p-hydroxybenzoic acid, m-hydroxybenzoicacid, dihydroxybenzoic acid (isomers), carboxydiphenol (isomers) and2-(4-hydroxyphenyl)-2-(3′-carboxy-4′-hydroxyphenyl)propane;aryloxycarbonyl-(hydroxy)-arenes, such as phenyl salicylate, phenylp-hydroxybenzoate, tolyl salicylate, tolyl p-hydroxybenzoate, phenyldihydroxybenzoate (isomers), tolyl dihydroxybenzoate (isomers), phenyldihydroxybenzoate (isomers), phenoxycarbonyldiphenol (isomers) and2-(4-hydroxyphenyl)-2-(3′-phenoxycarbonyl-4′-hydroxyphenyl)propane;alkoxycarbonyl-(hydroxy)-arenes, such as methyl salicylate, methylp-hydroxybenzoate, ethyl salicylate, ethyl p-hydroxybenzoate, methyldihydroxybenzoate (isomers), methoxycarbonyldiphenol (isomers) and2-(4-hydroxyphenyl)-2-(3′-methoxycarbonyl-4′-hydroxyphenyl)propane;aryloxycarbonyl-(alkoxy)-arenes, such as phenyl methoxybenzoate(isomers), tolyl methoxybenzoate (isomers), phenyl ethoxybenzoate(isomers), tolyl ethoxybenzoate (isomers), phenylhydroxy-methoxybenzoate (isomers),hydroxy-methoxy-(phenoxycarbonyl)-diphenyl (isomers),2-(4-methoxyphenyl)-2-(3′-phenoxycarbonyl-4′-hydroxyphenyl)propane and2-(4-hydroxyphenyl)-2-(3′-phenoxycarbonyl-4′-methoxyphenyl)propane;aryloxycarbonyl-(aryloxy)-arenes, such as phenyl phenoxybenzoate(isomers), tolyl phenoxybenzoate (isomers), tolyl tolyloxybenzoate(isomers), phenyl hydroxy-phenoxy-benzoate (isomers),hydroxyphenoxy-(phenoxycarbonyl)-diphenyl (isomers),2-(4-phenoxyphenyl)-2-(3′-phenoxycarbonyl-4′-hydroxyphenyl)propane and2-(4-hydroxyphenyl)-2-(3′-phenoxycarbonyl-4′-phenoxyphenyl)propane;alkoxycarbonyl-(alkoxy)-arenes, such as methyl methoxybenzoate(isomers), ethyl methoxybenzoate (isomers), methyl ethoxybenzoate(isomers), ethyl ethoxybenzoate (isomers), methylhydroxy-methoxybenzoate (isomers),hydroxy-methoxy-(methoxycarbonyl)-diphenyl (isomers),2-(4-methoxyphenyl)-2-(3′-methoxycarbonyl-4′-hydroxyphenyl)propane and2-(4-hydroxyphenyl)-2-(3′-methoxycarbonyl-4′-methoxyphenyl)propane;alkoxycarbonyl-(aryloxy)-arenes, such as methyl phenoxybenzoate(isomers), ethyl phenoxybenzoate (isomers), methyl tolyloxybenzoate(isomers), ethyl tolyloxybenzoate (isomers), phenylhydroxy-methoxy-benzoate (isomers),hydroxy-methoxy-(phenoxycarbonyl)-diphenyl (isomers),2-(4-methoxyphenyl)-2-(3′-phenoxycarbonyl-4′-hydroxyphenyl)propane and2-(4-hydroxyphenyl)-2-(3-phenoxycarbonyl-4′-methoxyphenyl)propane(isomers); aryloxycarbonyl-(aryloxycarbonyloxy)-arenes, such as phenylphenoxycarbonyloxybenzoate (isomers), tolyl phenoxycarbonyloxybenzoate(isomers), tolyl tolyloxycarbonyloxybenzoate (isomers), phenylhydroxy-phenoxycarbonyloxybenzoate (isomers),hydroxy-phenoxycarbonyloxy-(phenoxycarbonyl)-diphenyl (isomers),2-[4-(phenoxycarbonyloxy)phenyl]-2-(3′-phenoxycarbonyl-4′-hydroxyphenyl)propaneand2-(4-hydroxyphenyl)-2-[3′-phenoxycarbonyl-4′-(phenoxycarbonyloxy)phenyl]propane;aryloxycarbonyl-(alkoxycarbonyloxy)-arenes, such as phenylmethoxycarbonyloxybenzoate (isomers), tolyl methoxycarbonyloxybenzoate(isomers), phenyl ethoxycarbonyloxybenzoate (isomers), tolylethoxycarbonyloxybenzoate (isomers), phenylhydroxy-methoxycarbonyloxybenzoate (isomers),hydroxy-methoxycarbonyloxy-(phenoxycarbonyl)-diphenyl (isomers),2-[4-(methoxycarbonyloxy)phenyl]-2-(3′-phenoxycarbonyl-4′-hydroxyphenyl)propaneand2-(4-hydroxyphenyl)-2-[3′-phenoxycarbonyl-4′-(methoxycarbonyloxy)phenyl]propane;alkoxycarbonyl-(aryloxycarbonyloxy)-arenes, such as methylphenoxycarbonyloxybenzoate (isomers), ethyl phenoxycarbonyloxybenzoate(isomers), methyl tolyloxycarbonyloxybenzoate (isomers), ethyltolyloxycarbonyloxybenzoate (isomers), methylhydroxy-phenoxycarbonyloxy-benzoate (isomers),hydroxy-phenoxycarbonyloxy-(methoxycarbonyl)-diphenyl (isomers),2-[4-(phenoxycarbonyloxy)phenyl]-2-(3′-methoxycarbonyl-4′-hydroxyphenyl)propaneand2-(4-hydroxyphenyl)-2-[3′-methoxycarbonyl-4′-(phenoxycarbonyloxy)phenyl]propane;and alkoxycarbonyl-(alkoxycarbonyloxy)-arenes, such as methylmethoxycarbonyloxybenzoate (isomers), ethyl methoxycarbonyloxybenzoate(isomers), methyl ethoxycarbonyloxybenzoate (isomers), ethylethoxycarbonyloxybenzoate (isomers), methylhydroxy-methoxycarbonyloxybenzoate (isomers),hydroxy-methoxycarbonyloxy-(methoxycarbonyl)-diphenyl (isomers),2-[4-(methoxycarbonyloxy)phenyl]-2-(3′-methoxycarbonyl-4′-hydroxyphenyl)propaneand2-(4-hydroxyphenyl)-2-[3′-methoxycarbonyl-4′-(methoxycarbonyloxy)phenyl]propane.

Of these aromatic carboxy compounds and compounds having residues ofsuch aromatic carboxy compounds, attention should be made to those whichare likely to be present in the system for the transesterification forthe production of an aromatic carbonate. As such an aromatic carboxycompound and a compound having a residue of such an aromatic carboxycompound, there can be mentioned at least one member selected from thegroup consisting of:

(d) at least one member selected from the group consisting of a productproduced by the Fries rearrangement of an aromatic carbonate obtained bythe transesterification and a derivative of the product and

(e) at least one member selected from the group consisting of a productproduced by the Fries rearrangement of a reaction product obtained bythe transesterification of the aromatic polyhydroxy compound and aderivative of the product.

As mentioned above, in the process for producing aromatic carbonates ofthe present invention, the reactions of producing methyl phenylcarbonate and diphenyl carbonate from dimethyl carbonate and phenol areespecially important. Therefore, taking these reactions as examples,examples of aromatic carboxy compounds and compounds having residues ofsuch aromatic carboxy compounds, which are included in (d) and (e) aboveare enumerated below.

Examples of (d) include salicyclic acid, p-hydroxybenzoic acid, phenylsalicylate, phenyl p-hydroxybenzoate, methyl salicylate, methylp-hydroxybenzoate, phenyl methoxybenzoate (isomers), phenylphenoxybenzoate (isomers), phenyl phenoxycarbonyloxybenzoate (isomers),methyl phenoxycarbonyloxybenzoate (isomers), methylmethoxycarbonyloxybenzoate (isomers).

Examples of (e) include dihydroxybenzoic acid (isomers), phenyldihydroxybenzoate (isomers), phenoxycarbonyldiphenol (isomers),2-(4-hydroxyphenyl)-2-(3′-phenoxycarbonyl-4′-hydroxyphenyl)propane.

Examples of xanthones belonging to the high boiling point substances inthe present invention include xanthone and those in which the aromaticring of xanthone is substituted with at least one substituent selectedfrom the group consisting of an alkyl group, such as methyl, ethyl,propyl, isopropyl, butyl, iso-butyl and the like; a hydroxy group; analkoxy group, such as methoxy, ethoxy, propoxy, isopropoxy, butoxy andthe like; aryloxy group, such as phenoxy, tolyloxy and the like; analkoxycarbonyloxy group, such as methoxycarbonyloxy, ethoxycarbonyloxy,propoxycarbonyloxy, butoxycarbonyloxy and the like; anaryloxycarbonyloxy group, such as phenoxycarbonyloxy,tolyloxycarbonyloxy and the like; a carboxy group; an alkoxycarbonylgroup, such as methoxycarbonyl, ethoxycarbonyl and the like; anaryloxycarbonyl group, such as phenoxycarbonyl, tolyloxycarbonyl and thelike; an arylcarbonyloxy group, such as benzoyloxy, tolylcarbonyloxy andthe like.

The functional substance (C) used in the present invention is asubstance which is capable of reacting with at least one componentselected from the group consisting of the high boiling point substance(A) and the metal-containing catalyst (B). There is no particularlimitation with respect to the functional substance (C), as long as thesubstance is capable of forming at least one reaction product selectedfrom the group consisting of an (A)/(C) reaction product {which is areaction product of the functional substance (C) with the high boilingpoint substance (A)} and a (B)/(C) reaction product {which is a reactionproduct of the functional substance (C) with the metal-containingcatalyst (B)}. Examples of such a functional substance (C) includeoxidizing agents, reducing agents, precipitants, adsorbents and reactivesolvents. Of these, oxidizing agents, precipitants and reactive solventsare preferred. Further, these functional substances may be usedindividually, or at least two different functional substances may besimultaneously or stepwise added to the taken-out catalyst-containingliquid. Further, the reaction of the functional substance (C) with thehigh boiling point substance (A) and/or the metal-containing catalyst(B) can be carried out in a batchwise or a continuous manner.

In the present invention, when the functional substance (C) is capableof reacting with the high boiling point substance (A), the (A)/(C)reaction product is a product formed by the reaction between the highboiling point substance (A) and the functional substance (C). However,when the functional substance (C) is not capable of reacting with thehigh boiling point substance (A), the unreacted high boiling pointsubstance (A) is regarded as the (A)/(C) reaction product. On the otherhand, when the functional substance (A) is capable of reacting with themetal-containing catalyst (B), the (B)/(C) reaction product is a productformed by the reaction between the metal-containing catalyst (B) and thefunctional substance (C). However, when the functional substance (C) isnot capable of reacting with the metal-containing catalyst (B), theunreacted metal-containing catalyst (B) is regarded as the (B)/(C)reaction product.

In the present invention, the (A)/(C) reaction product is withdrawn fromthe production system for the desired aromatic carbonates, whereas the(B)/(C) reaction product is recycled to the reaction system comprisingthe starting material and the reactant. The withdrawal of the (A)/(C)reaction product can be carried out, for example, by separating the(A)/(C) reaction product from the (B)/(C) reaction product during and/orafter the reaction of the high boiling point substance (A) with thefunctional substance (C).

With respect to the method for separating the (A)/(C) reaction productfrom the (B)/(C) reaction product, any methods can be employed as longas the catalyst-containing liquid can be separated into a componentwhich is composed mainly of the (A)/(C) reaction product and a componentwhich is composed mainly of the (B)/(C) reaction product. Examples ofsuch separation methods include a gas phase-condensed phase separationmethod, such as a gas phase-liquid phase separation method, a gasphase-solid phase separation method or a gas phase-solid/liquid mixedphase separation method; a solid phase-liquid phase separation method,such as sedimentation, centrifugation or filtration; a distillationmethod; an extraction method; and an adsorption method. Of these, thesedimentation, the distillation and the adsorption method are preferred.These separation methods can be employed individually, or at least twoof such separation methods can be simultaneously or stepwise employed.

With respect to the combination of the functional substance (C) and theseparation method, there is no particular limitation. However, examplesof the preferred modes usable for practicing the method of the presentinvention, in which specific combinations of the functional substance(C) and the separation method are used, include:

(I) a mode in which the functional substance (C) is an oxidizing agent,so that an oxidation reaction is performed with respect to thecatalyst-containing liquid, in which the (A)/(C) reaction product is alow boiling point oxidation product and the (B)/(C) reaction product isa metal oxide; and the separation method is the gas phase-condensedphase separation method,

(II) a mode in which the functional substance (C) is a precipitant, sothat a precipitation reaction is performed with respect to thecatalyst-containing liquid, in which the (B)/(C) reaction product is ametal-containing substance which precipitates; and the separation methodis the solid-liquid separation method,

(III) a mode in which the functional substance (C) is a reactivesolvent, so that a solvolysis reaction is performed with respect to thecatalyst-containing liquid, in which the (A)/(C) reaction product is alow-boiling point solvolysis product; and the separation method is thedistillation method.

When the preferred mode of item (I) above is employed, use is made of anoxidizing agent which not only can oxidize the high boiling pointsubstance (A) to form a low boiling point oxidation product as the(A)/(C) reaction product, but also can oxidize the metal-containingcatalyst (B) to form a metal oxide as the (B)/(C) reaction product.Examples of oxidizing agents include air; molecular oxygen; ozone;hydrogen peroxide; silver oxide; organic peroxides, such as peraceticacid, perbenzoic acid, benzoyl peroxide, tert-butyl hydroperoxide andcumyl hydroperoxide; oxo-acids, such as nitrous acid, nitric acid,chloric acid, hypochlorous acid; and salts thereof. Of these, air,molecular oxygen, ozone, hydrogen peroxide, nitrous acid and nitric acidare preferred, and air and molecular oxygen are more preferred.

The type of the reaction performed in the catalyst-containing liquidusing the oxidizing agent varies depending on the type of the oxidizingagent and the reaction conditions. However, the reaction is performed ina phase selected from the group consisting of a liquid phase, agas-liquid mixed phase and a gas-liquid/solid mixed phase. The reactiontemperature varies depending on the type of the oxidizing agent;however, the reaction temperature is generally in the range of from −30to 2,000° C., preferably from 0 to 1,200° C., more preferably from 0 to900° C. The reaction time varies depending on the type of the oxidizingagent and the reaction temperature; however, the reaction time isgenerally in the range of from 0.001 to 100 hours, preferably from 0.1to 20 hours. The reaction pressure is generally in the range of from 10to 10⁷ Pa, preferably 10² to 3×10⁶ Pa. The reaction can be performed ineither a batchwise or a continuous manner.

In the preferred mode of item (I) above, the gas phase-condensed phaseseparation method is employed to separate the (A)/(C) reaction productfrom the (B)/(C) reaction product. The condensed phase means a liquidphase, a solid phase or a solid/liquid mixed phase. In the case wherethe oxidation reaction mixture obtained at the completion of theoxidation reaction forms a liquid phase, a gas/liquid mixed phase or agas/solid/liquid mixed phase, the reaction mixture is separated into agas phase composed mainly of a low boiling point oxidation product and acondensed phase containing a metal oxide. Then, by distilling off orevaporating the low boiling point oxidation product from the separatedcondensed phase, a metal oxide-rich condensed phase (composed mainly ofthe metal oxide) can be obtained. Alternatively, when the metal oxide(formed by the oxidation of the metal-containing catalyst (B) which isconducted with respect to the catalyst-containing liquid) forms a solidphase during the oxidation reaction, it is possible to obtain a reactionmixture in the form of a liquid-solid mixture. Further, during theoxidation reaction, the low boiling point oxidation product formed byoxidation of the high boiling point substance (A) may be evaporatedtogether with the volatile components of the liquid reaction system, tothereby obtain a solid reaction mixture. This method is preferred,because it becomes possible to separate the oxidation reaction systeminto the solid phase composed mainly of the metal oxide and the gasphase containing the low boiling point oxidation product whileperforming the oxidation reaction.

The “low boiling point oxidation product” means compounds having aboiling point lower than that of the high boiling point substance (A),which are formed by oxidation of the high boiling point substance (A)using the oxidizing agent. The type of the low boiling point oxidationproduct varies depending on the type of the oxidizing agent and the typeof the high boiling point substance (A). Examples of low boiling pointoxidation products include carbon dioxide, water, carbon monoxide,oxygen-containing organic compounds, unsaturated organic compounds,compounds formed by the decomposition of the high boiling pointsubstance.

The “metal oxide” means an oxide of the metal of the metal-containingcatalyst (B). A single type of the metal-containing catalyst (B) mayform different metal oxides depending on the oxidation reactionconditions and the type of the metal contained in the catalyst (B).Specific examples of metal oxides include PbO, PbO₂, Pb₃O₄, CuO, Cu₂O,Li₂O, ZnO, CdO, FeO, Fe₃O₄, Fe₂O₃, CoO, Co₃O₄, Co₂O₃, CoO₂, NiO, ZrO₂,Al₂O₃, TiO, Ti₂O₃, TiO₂, SnO and SnO₂. When the metal-containingcatalyst (B) contains a plurality of different metals, there is or areobtained a mixture of metal oxides corresponding to the metals containedin the catalyst (B) or/and a compound metal oxide.

When the preferred mode of item (II) above is employed, there is noparticular limitation with respect to the metal-containing substanceformed as the (B)/(C) reaction product, as long as the metal-containingsubstance is present in a solid state in the precipitation reactionmixture, and contains the metal. Examples of metal-containing substancesinclude metal hydroxides; metal chalcogenides, such as a metal oxide anda metal sulfide; salts of inorganic acids, such as a metal carbonate anda metal sulfate; metal salts of organic acids; metal complexes; andmetal double salts.

Of these, from the viewpoint of the low solubility in the reactionmixture, a metal carbonate, a metal hydroxide, a metal oxide, a metalsulfide and a metal sulfate are preferred. Each of the metal-containingsubstances may contain other substance (such as the reactant, thestarting material and the high boiling point substance) coordinatedthereto.

With respect to the precipitant, there is no particular limitation, aslong as the precipitant can react with the metal-containing catalyst (B)to form the above-mentioned metal-containing substance. For example, forprecipitating metal hydroxides, use can be made of inorganic hydroxides(such as a hydroxide of an alkali metal or an alkaline earth metal) andwater; for precipitating metal oxides, use can be made of inorganicoxides (such as an oxide of an alkali metal or an alkaline earth metal)and oxidizing agents (such as hydrogen peroxide); for precipitatingmetal sulfides, use can be made of inorganic sulfides (such as a sulfideof an alkali metal or an alkaline earth metal) and hydrogen sulfide; forprecipitating metal carbonates, use can be made of inorganic carbonates(such as a carbonate of an alkali metal or an alkaline earth metal),carbonic acid and carbon dioxide with water; for precipitating metalsulfates, use can be made of inorganic sulfates (such as a sulfate of analkali metal or an alkaline earth metal), sulfuric acid and sulfurtrioxide with water.

The type of the reaction between the metal-containing catalyst (B) andthe precipitant varies depending on the type of the catalyst, the typeof the precipitant, the reaction conditions and the like. However, thereaction is generally performed in a phase selected from the groupconsisting of a liquid phase, a liquid-gas mixed phase, agas-liquid-solid mixed phase and a solid-liquid mixed phase. Thereaction temperature varies depending on the type of the precipitant;however, the reaction temperature is generally in the range of from −70to 600° C., preferably from −30 to 400° C., more preferably from −10 to250° C. The reaction time varies depending on the type of theprecipitant and the reaction temperature; however, the reaction time isgenerally in the range of from 0.001 to 100 hours, preferably from 0.1to 20 hours. The reaction pressure is generally in the range of from 10to 10⁷ Pa. The above-mentioned reaction can be performed in either abatchwise manner or a continuous manner.

In the present invention, it is preferred to add a substance whichserves as a crystal nucleus to the precipitation reaction system. At thetime of the separation of the metal-containing substance from theprecipitation reaction mixture, the metal-containing substance needs tobe in a solid state. However, the metal-containing substance need not bein a solid state during the precipitation reaction, as long as themetal-containing substance becomes a solid by a cooling operation, etc.after the completion of the reaction.

In the preferred mode of item (II) above, the solid phase-liquid phaseseparation method is employed to separate the (A)/(C) reaction productfrom the (B)/(C) reaction product. Specifically, the precipitationreaction mixture is separated into a solid phase composed mainly of ametal-containing substance and a liquid phase composed mainly ofsubstances originating from a high boiling point substance. The solidphase-liquid phase separation method is generally conducted bysedimentation, centrifugation, filtration or the like.

Further, in the preferred mode of item (II) above, the high boilingpoint substance (A) contained in the catalyst-containing liquid does notundergo the precipitation reaction with the functional substance (C)[therefore, in this preferred mode, the unreacted component (A), whichis not precipitated when the functional substance (C) is added, isregarded as the (A)/(C) reaction product]; however, the high boilingpoint substance (A) may undergo a reaction other than the precipitationreaction during the precipitation reaction of the metal-containingcatalyst (B).

When the preferred mode of item (III) above is employed, there is noparticular limitation with respect to the reactive solvent, as long asthe reactive solvent can react with the high boiling point substance (A)to form compounds having a boiling point lower than the boiling point ofthe high boiling point substance (A). Examples of reactive solventsinclude water; lower alcohols, such as methanol, ethanol, propanol(isomer) and butanol (isomer); lower carboxylic acids, such as formicacid, acetic acid and propionic acid; and carbonates, such as dimethylcarbonate and diethyl carbonate. Of these, water, methanol, ethanol,acetic acid, methyl acetate, ethyl acetate, dimethyl carbonate, diethylcarbonate and the like are preferred, and water is more preferred.

In the present invention, the “solvolysis” means the decompositionreaction of the high boiling point substance (A) with the reactivesolvent. The reaction product obtained by the solvolysis may besubjected to further reaction other than the solvolysis, such as thedecarboxylation and the like.

With respect to the low boiling point product obtained by thesolvolysis, there is no particular limitation, as long as the lowboiling point product has a boiling point lower than the boiling pointof the high boiling point substance (A). The type and structure of thelow boiling point product vary depending on the type of the reactivesolvent and the type of the high boiling point substance (A). Withrespect to the relationship between the reactive solvent, the highboiling point substance (A) and the low boiling point product, specificexplanation is made below, taking as an example the case where the highboiling point substance (A) is phenyl salicylate which is one of thearomatic carboxy compounds.

(i) When the reactive solvent is water, phenol and salicylic acid areformed by the hydrolysis, and the formed salicylic acid undergoesdecarboxylation to form phenol and carbon dioxide.

(ii) When the reactive solvent is an alcohol, an alkyl salicylate andphenol are formed by alcoholysis.

(iii) When the reactive solvent is a carboxylic acid, salicylic acid anda phenyl carboxylate are formed by transesterification, and the formedsalicylic acid undergoes decarboxylation to form phenol and carbondioxide.

As mentioned above, the above explanation is made, taking as an examplephenyl salicylate, which has a relatively simple structure as anaromatic carboxy compound. However, also in the case of an aromaticcarboxy compound having a more complicated structure, the same types ofreactions as mentioned in items (i) to (iii) above occur. Therefore, asthe reaction products corresponding to those mentioned in items (i) to(iii) above, there can be obtained, for example, an aromatic hydroxycompound, such as an aromatic monohydroxy compound; a lower carboxylicacid ester of an aromatic monohydroxy compound; an ester of an aromaticcarboxy compound with a lower alcohol; and carbon dioxide. Of theabove-mentioned reaction products obtained by the solvolysis, thearomatic monohydroxy compound is especially preferred, because thisproduct is a reactant used in the present invention so that this productcan be recycled.

The catalyst-containing liquid contains the metal-containing catalyst(B), and the catalyst (B) generally also serves as a catalyst for thesolvolysis. Therefore, it is not necessary to specifically use acatalyst for the solvolysis, but such a catalyst for the solvolysis canbe used for the purpose of improving the reaction rate, etc.

The type of the reaction between the high boiling point substance (A)and the reactive solvent varies depending on the reaction conditions;however, the reaction is generally performed in a phase selected fromthe group consisting of a liquid phase and a solid-liquid mixed phase.The reaction temperature varies depending on the type of the reactivesolvent; however, the reaction temperature is generally in the range offrom −30 to 400° C., preferably from −10 to 300° C., more preferablyfrom 0 to 250° C. The reaction time varies depending on the type of thereactive solvent and the reaction temperature; however, the reactiontime is generally in the range of from 0.001 to 100 hours, preferablyfrom 0.1 to 20 hours. The reaction pressure is generally in the range offrom 10 to 10⁷ Pa. The reaction can be performed in either a batchwisemanner or a continuous manner.

The metal-containing catalyst (B) may or may not undergo the solvolysis[therefore, in this preferred mode, when the metal-containing catalyst(B) does not undergo the solvolysis, the unreacted component (B), whichis not solvolyzed with the functional substance (C), is regarded as the(B)/(C) reaction product]. In the case where water or an alcohol is usedas a reactive solvent so as to solvolyze an aromatic carboxy compoundcontained as the high boiling point substance (A) in thecatalyst-containing liquid, a decarboxylation reaction occurssimultaneously with the solvolysis, so that carbon dioxide is formed asone of the reaction products originating from the high boiling pointsubstance (A). Therefore, it is possible that the formed carbon dioxideserves as a precipitant and reacts with the metal-containing catalyst(B) to there-by form a metal-containing substance (such as a metalcarbonate) in the form of a solution thereof and/or in the form of asolid.

In the preferred mode of item (III) above, the separation of the (A)/(C)reaction product from the (B)/(C) reaction product is conducted by adistillation method, wherein a low boiling point product formed as the(A)/(C) reaction product by the solvolysis is removed from thesolvolysis reaction mixture as a distillate. The (B)/(C) reactionproduct is contained in the liquid remaining in the distillation columnemployed. The distillation temperature is generally in the range of from10 to 300° C., preferably from 50 to 250° C., in terms of thetemperature of the liquid in the distillation column. The distillationpressure is generally in the range of from 0.1 to 1.0×10⁶ Pa, preferablyfrom 1.0 to 1.0×10⁵ Pa. The distillation can be conducted either in abatchwise manner or a continuous manner.

The recycling of the (B)/(C) reaction product to the reaction system canbe conducted by a method in which the (B)/(C) reaction product, whichhas been separated from the (A)/(C) reaction product and which is in theform of a liquid, a solid or a liquid-solid mixture, as such, isrecycled to the reaction system. Alternatively, when the (B)/(C)reaction product is obtained in such a form as contains other componentsthan the reaction product, the recycling of the (B)/(C) reaction productcan be conducted by a method in which a part or all of such othercomponents are separated from the other components-containing (B)/(C)reaction product, and the resultant is recycled to the reaction system.Further, the recycling of the (B)/(C) reaction product can be conductedby a method in which the separated (B)/(C) reaction product is mixedand/or reacted with the starting material or the reactant, and theresultant (i.e., a liquid reaction mixture, a slurry, etc.) is recycledto the reaction system. This method is advantageous when the (B)/(C)reaction product is in the form of a solid or a solid-liquid mixture.The recycling of the (B)/(C) reaction product to the reaction system canbe conducted in either a batch-wise manner or in a continuous manner.

As mentioned above, the method of the present invention comprises:

taking out at least one type of catalyst-containing liquid which isselected from the group consisting of:

a portion of the high boiling point reaction mixture obtained by thetransesterification reaction before the separation of the high boilingpoint reaction mixture into the product fraction and the liquid catalystfraction, and

a portion of the separated liquid catalyst fraction,

each portion containing at least one high boiling point substance (A)having a boiling point higher than the boiling point of the producedaromatic carbonate and containing the metal-containing catalyst (B); and

adding to the taken-out catalyst-containing liquid a functionalsubstance (C) capable of reacting with at least one component selectedfrom the group consisting of the component (A) and the component (B).

With respect to the amount of the portion of the high boiling pointreaction mixture, which is taken out as the catalyst-containing liquid,the amount is from 0.01 to 10% by weight, preferably from 0.1 to 5% byweight, more preferably from 0.3 to 1% by weight, based on the weight ofthe high boiling point reaction mixture. On the other hand, with respectto the amount of the portion of the separated liquid catalyst fraction,which is taken out as the catalyst-containing liquid, the amount is from0.01 to 40% by weight, preferably from 0.1 to 20% by weight, morepreferably from 1 to 10% by weight, based on the weight of the separatedliquid catalyst fraction.

With respect to the concentration of the high boiling point substance(A) in the taken-out catalyst-containing liquid, the concentrationvaries depending on the type of the high boiling point substance (A).However, too low a concentration of the high boiling point substance (A)is not preferable, since the amount of the taken-out catalyst-containingliquid becomes too large. On the other hand, too high a concentration ofthe high boiling point substance (A) is also not preferable, since theboiling point and viscosity of the taken-out catalyst-containing liquidbecome too high, so that the handling of the taken-outcatalyst-containing liquid becomes difficult. Therefore, theconcentration of the high boiling point substance (A) in the taken-outcatalyst-containing liquid is generally from 0.01 to 99% by weight,preferably from 0.1 to 95% by weight, more preferably from 1 to 90% byweight.

Further, when the high boiling point substance (A) is an aromaticpolyhydroxy compound, for preventing the catalyst from depositing on oradhering to the inner walls of the reactor, the pipes and the like, itis preferred that the taken-out catalyst-containing liquid contains thearomatic polyhydroxy compound and the metal-containing catalyst inamounts such that the weight ratio of the aromatic polyhydroxy compoundto the metal of the catalyst becomes 2.0 or less.

With respect to the separation of the desired aromatic carbonate fromthe product fraction (separated from the high boiling point reactionmixture obtained by the transesterification reaction) comprising thearomatic carbonate, the unreacted starting material and the unreactedreactant, the separation can be easily conducted by a conventionalseparation method, such as a distillation method.

In the present invention, the purity of the aromatic carbonate which hasbeen separated from the product fraction can be calculated by thefollowing formula:$\text{Purity of the aromatic carbonate~~(\%)} = {\frac{\text{the aromatic carbonate (\%~~by weight)}}{100 - \text{the unreacted starting material~~(\%~~by weight)} - \text{~~~~~~~the unreacted reacting material~~(\%~~by weight)}} \times 100}$

The purity of the aromatic carbonate obtained by the process of thepresent invention is generally 99% or more, preferably 99.5% or more,most preferably 99.8% or more.

In a further preferred aspect of the present invention, there isprovided a mode of the above-mentioned process of the present invention,in which the above-mentioned steps (1), (2) and (3) are continuouslyconducted. That is, in this mode of the process, the following steps arecontinuously conducted:

(1) transesterifying, in the presence of a metal-containing catalyst, astarting material selected from the group consisting of a dialkylcarbonate, an alkyl aryl carbonate and a mixture thereof with a reactantselected from the group consisting of an aromatic monohydroxy compound,an alkyl aryl carbonate and a mixture thereof, to thereby obtain a highboiling point reaction mixture comprising the metal-containing catalystand at least one aromatic carbonate, while withdrawing a low boilingpoint reaction mixture which contains a low boiling point by-productcomprising an aliphatic alcohol, a dialkyl carbonate or a mixturethereof,

(2) separating the high boiling point reaction mixture into a productfraction comprising the produced aromatic carbonate and a liquidcatalyst fraction comprising the metal-containing catalyst, and

(3) recycling the liquid catalyst fraction to the reaction system whilewithdrawing the product fraction, thereby enabling continuous productionof the aromatic carbonate.

In this preferred mode for continuously producing the aromaticcarbonate, it is especially preferred that the step (1) of the processof the present invention is performed as follows: the starting materialand the reactant are continuously fed to a continuous multi-stagedistillation column to effect a transesterification reactiontherebetween in at least one phase selected from the group consisting ofa liquid phase and a gas-liquid phase in the presence of ametal-containing catalyst, wherein a high boiling point reaction mixturecontaining the produced aromatic carbonate is withdrawn in a liquid formfrom a lower portion of the distillation column, while continuouslywithdrawing a low boiling point reaction mixture containing the lowboiling point by-product in a gaseous form from an upper portion of thedistillation column by distillation.

In another aspect of the present invention, there is provided a processfor producing an aromatic polycarbonate, which comprises polymerizingthe high purity diaryl carbonate obtained by the process of the presentinvention with an aromatic dihydroxy compound by transesterification.

With respect to the method for producing the aromatic polycarbonate bytransesterification, reference can be made to, for example, U.S. Pat.No. 5,589,564. By the use of the diaryl carbonate obtained by theprocess of the present invention, it has become possible to perform thepolymerization at a high rate. Further, the aromatic polycarbonateobtained by the transesterification reaction between the aromaticdihydroxy compound and the diaryl carbonate obtained by the process ofthe present invention is a high quality aromatic polycarbonate which isfree from the discoloration.

The aromatic dihydroxy compound, which can be used for producing thearomatic polycarbonate by transesterification, can be represented by thefollowing formula:

HO—Ar′—OH

wherein Ar′ represents a divalent aromatic group having from 5 to 200carbon atoms.

Preferred examples of divalent aromatic groups Ar′ having from 5 to 200carbon atoms include an unsubstituted or substituted phenylene group, anunsubstituted or substituted naphthylene group, an unsubstituted orsubstituted biphenylene group and an unsubstituted or substitutedpyridylene group. Further examples of such divalent aromatic groupsinclude divalent groups, each represented by the following formula:

—Ar^(1′)—Y —Ar^(2′)

wherein each of Ar^(1′) and Ar^(2′) independently represents a divalentcarbocyclic or heterocyclic aromatic group having from 5 to 70 carbonatoms, and Y′ represents a divalent alkane group having from 1 to 30carbon atoms.

In the divalent aromatic groups Ar^(1′) and Ar^(2′), at least onehydrogen atom may be substituted with a which does not adversely affectthe reaction, such as a halogen atom, an alkyl group having from 1 to 10carbon atoms, an alkoxy group having from 1 to 10 carbon atoms, a phenylgroup, a phenoxy group, a vinyl group, a cyano group, an ester group, anamide group and a nitro group.

Illustrative examples of heterocyclic aromatic groups include anaromatic group having at least one hetero atom, such as a nitrogen atom,an oxygen atom or a sulfur atom.

Examples of divalent aromatic groups Ar^(1′) and Ar^(2′) include anunsubstituted or substituted phenylene group, an unsubstituted orsubstituted biphenylene group and an unsubstituted or substitutedpyridylene group. Substituents for Ar^(1′) and Ar^(2′) are as describedabove.

Examples of divalent alkane groups Y′ include organic groupsrespectively represented by the following formulae:

wherein each of R^(3′), R^(4′), R^(5′) and R^(6′) independentlyrepresents a hydrogen atom, an alkyl group having from 1 to 10 carbonatoms, an alkoxy group having from 1 to 10 carbon atoms, a cycloalkylgroup having from 5 to 10 ring-forming carbon atoms, a carbocyclicaromatic group having from 5 to 10 ring-forming carbon atoms and acarbocyclic aralkyl group having from 6 to 10 ring-forming carbon atoms;k′ represents an integer of from 3 to 11; each X′ represents a carbonatom and has R^(7′) and R^(8′) bonded thereto; each R^(7′) independentlyrepresents a hydrogen atom or an alkyl group having from 1 to 6 carbonatoms, and each R^(8′) independently represents a hydrogen atom or analkyl group having from 1 to 6 carbon atoms, wherein R^(7′) and R^(8′)are the same or different;

wherein at least one hydrogen atom of each of R^(3′), R^(4′), R^(5′),R^(6′), R^(7′) and R^(8′) may be independently replaced by a substituentwhich does not adversely affect the reaction, such as a halogen atom, analkyl group having from 1 to 10 carbon atoms, an alkoxy group havingfrom 1 to 10 carbon atoms, a phenyl group, a phenoxy group, a vinylgroup, a cyano group, an ester group, an amide group and a nitro group.

Specific examples of divalent aromatic groups Ar′ include groupsrespectively represented by the following formulae:

wherein each of R^(9′) and R^(10′) independently represents a hydrogenatom, a halogen atom, an alkyl group having from 1 to 10 carbon atoms,an alkoxy group having from 1 to 10 carbon atoms, a cycloalkyl grouphaving from 5 to 10 ring-forming carbon atoms, or an allyl group havingfrom 6 to 30 carbon atoms; each of m′ and n′ independently represents aninteger of from 1 to 4, with the proviso that when m′ is an integer offrom 2 to 4, R^(9′)'s are the same or different, and when n′ is aninteger of from 2 to 4, R^(10′)'s are the same or different.

Further, examples of divalent aromatic groups Ar′ also include thosewhich are represented by the following formula:

—Ar^(1′)—Z—Ar^(2′)—

wherein Ar^(1′) and Ar^(2′) are as defined above; and Z′ represents asingle bond or a divalent group, such as —O—, —CO—, —S—, —SO₂, —SO—,—COO—, or —CON(R^(3′))—, wherein R^(3′) is as defined above.

Examples of such divalent aromatic groups Ar′ include groupsrespectively represented by the following formulae:

wherein R^(9′), R^(10′), m′ and n′ are as defined above.

The above-mentioned aromatic dihydroxy compounds can be usedindividually or in combination. Representative examples of aromaticdihydroxy compounds include bisphenol A.

With respect to the material of an apparatus used for producing thearomatic polycarbonate, there is no particular limitation. However,stainless steel, glass or the like is generally used as a material forat least the inner walls of the apparatus.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinbelow, the present invention will be described in more detail withreference to the following Examples and Comparative Examples, but theyshould not be construed as limiting the scope of the present invention.

In the following Examples and Comparative Examples, various measurementswere conducted in accordance with the following methods.

The metal concentration of a metal-containing catalyst was measured bymeans of an ICP (inductively coupled plasma emission spectral analyzer)(JY38PII: manufactured and sold by Seiko Electronics Co, Ltd., Japan).

The concentration of an organic matter in a liquid was measured by gaschromatography.

The concentration of a high boiling point substance (A) coordinated to ametal-containing catalyst in a catalyst-containing liquid was measuredby a method in which a ligand exchange with trifluoroacetic acid isconducted, followed by analysis by gas chromatography.

The total concentration of both high boiling point substances (A)coordinated to and not coordinated to a metal-containing catalyst in acatalyst-containing liquid was determined as follows. Thecatalyst-containing liquid was subjected to distillation using a smallsize distillation column and the total of the weight of a fractionhaving a boiling point higher than that of a desired aromatic carbonateand the weight of an organic matter contained in the distillationresidue remaining in the distillation column was calculated. Then, theweight percentage of the thus calculated total weight, based on theweight of the catalyst-containing liquid, was obtained, and the obtainedweight percentage was taken as the total concentration of both highboiling point substances (A) coordinated to and not coordinated to ametal-containing catalyst in the catalyst-containing liquid.

The number average molecular weight of a produced aromatic polycarbonatewas measured by gel permeation chromatography (GPC) (apparatus:HLC-8020, manufactured and sold by Tosoh Corp., Japan; column: TSK-GEL,manufactured and sold by Tosoh Corp., Japan; solvent: tetrahydrofuran).

All of the concentrations are indicated by weight percentages.

EXAMPLE 1 Preparation of Catalyst

A mixture of 40 kg of phenol (hereinafter, frequently referred to as“PhOH”) and 8 kg of lead monoxide was heated to and maintained at 180°C. for 10 hours, thereby performing a reaction. After that period oftime, water formed in the resultant reaction mixture was distilled offtogether with unreacted phenol, to thereby obtain catalyst I.

Production of Aromatic Carbonate

The production of an aromatic carbonate was conducted using the systemas shown in FIG. 1, which comprises continuous multi-stage distillationcolumn 1 having a height of 6 m and a diameter of 6 inches and equippedwith 20 sieve trays.

A mixture of dimethyl carbonate (hereinafter, frequently referred to as“DMC”), phenol (which contains, as an impurity, 30 ppm by weight of4,4′-dihydroxydiphenyl which is a high boiling point substance) andcatalyst I was continuously fed in liquid form from conduit 3 throughpreheater 4 and conduit 5 into continuous multi-stage distillationcolumn 1 at a position of 0.5 m below top 2 thereof at a rate of 32kg/hr, and was allowed to flow down inside multi-stage distillationcolumn 1, thereby performing a reaction. The weight ratio of thedimethyl carbonate to the phenol in the mixture was 62/38, and catalystI was used in an amount such that the Pb concentration of the reactionmixture in conduit 13 became 0.038% by weight, wherein the Pbconcentration can be confirmed using a sample withdrawn through asampling nozzle (not shown) provided on conduit 13. Dimethyl carbonatewas fed from conduit 7 into evaporator 8 thereby forming a gas and theformed gas of dimethyl carbonate was fed through conduit 9 to bottom 6of continuous multi-stage distillation column 1 at a rate of 26 kg/hr.The reaction conditions of the above reaction were such that thetemperature at the bottom of continuous multi-stage distillation column1 was 203° C. and the pressure at the top of continuous multi-stagedistillation column 1 was 7.4×10⁵ Pa. Gas distilled from column top 2was led through conduit 10 into condenser 11, in which the gas wascondensed. The resultant condensate was continuously withdrawn at a rateof 25 kg/hr through conduit 12. A reaction mixture [containing methylphenyl carbonate (as a desired reaction product) (hereinafter,frequently referred to as “MPC”), the catalyst, and high boiling pointsubstances] was continuously withdrawn from column bottom 6 at a rate of34 kg/hr and led into evaporator 14 through conduit 13, from which anevaporated gas containing the methyl phenyl carbonate was withdrawn andled through conduit 21 into condenser 22, in which the gas wascondensed. The resultant condensate was withdrawn from condenser 22through conduit 23, wherein the condensate withdrawal rate during theperiod of time of 400 hours from the start of the operation, thecondensate withdrawal rate during the period of time of from 400 hoursto 600 hours after the start of the operation and the condensatewithdrawal rate during the period of time of from 600 hours to 5,000hours after the start of the operation were 32.95 kg/hr, 32.99 kg/hr and33 kg/hr, respectively. On the other hand, an evaporation-concentratedliquid containing the catalyst and high boiling point substances wasformed in evaporator 14. A portion of the concentrated liquid was ledinto reboiler 17 through conduits 15 and 16 and recycled into evaporator14 through conduit 18. The remainder of the concentrated liquid inevaporator 14 was recycled into continuous multi-stage distillationcolumn 1 at a rate of 1 kg/hr through conduits 15, 19 and 3. After thestart of the recycling of the concentrated liquid into continuousmulti-stage distillation column 1 through conduits 15, 19 and 3, thefeeding rate of the mixture of dimethyl carbonate, phenol and catalyst Ithrough conduit 3 into continuous multi-stage distillation column 1 wasappropriately controlled according to the recycling rate of theconcentrated liquid.

During the period of time of from 400 hours to 5,000 hours after thestart of the operation, a portion of the concentrated liquid formed inevaporator 14 was continuously withdrawn through conduit 20 at a rate of0.05 kg/hr and led into thin-film evaporator 33 thereby forming anevaporated gas. At a point in time of 400 hours after the start of theoperation, a sample (of the concentrated liquid withdrawn fromevaporator 14) was taken through a sampling nozzle (not shown) providedon conduit 15′, and was analyzed to determine the composition of theconcentrated liquid by the above-mentioned methods. The concentratedliquid had the following composition: Pb (which is the metal componentof catalyst I): 1.3% by weight; the total concentration of high boilingpoint substances: 1.7% by weight; and 4,4′-dihydroxydiphenyl (which is ahigh boiling point substance): 0.7% by weight. The evaporated gas formedin thin-film evaporator 33 was continuously withdrawn therefrom throughconduit 35 at a rate of 0.04 kg/hr and recycled through conduit 49 intothe system for the transesterification. On the other hand, anevaporation-concentrated liquid containing the catalyst and high boilingpoint substances was continuously withdrawn from the bottom of thin-filmevaporator 33 through conduit 34 at a rate of 0.01 kg/hr and led intostorage vessel 36. A sample (of the evaporation-concentrated liquidwithdrawn from thin-film evaporator 33) was taken through a samplingnozzle (not shown) provided on conduit 34 at a point in time of 400hours after the start of the operation, and was analyzed to determinethe composition of the evaporation-concentrated liquid by theabove-mentioned methods. The evaporation-concentrated liquid had thefollowing composition: Pb (which is the metal component of catalyst I):6.5% by weight; the total concentration of high boiling pointsubstances: 8.6% by weight; and 4,4′-dihydroxydiphenyl (which is a highboiling point substance): 3.6% by weight. At a point in time of 550hours after the start of the operation, 1 kg of the concentrated liquidstored in storage vessel 36 was withdrawn and led into electric furnace38 through conduit 37. In electric furnace 38, the concentrated liquidwas heated to and maintained at 700° C. for 8 hours while introducingair into electric furnace 38 from conduit 39, to thereby oxidize theconcentrated liquid under atmospheric pressure. The resultant oxidationproducts (i.e., carbon dioxide, water and low boiling point organiccompounds) derived from organic matter contained in the concentratedliquid were withdrawn through waste product conduit 40. The oxidationproducts remaining in electric furnace 38 were allowed to cool and,then, a sample of the remaining oxidation products was taken out fromelectric furnace 38 and analyzed. By the analysis, only lead monoxide,derived from catalyst I, was detected. This means that, by the oxidativereaction of the concentrated liquid, the organic matter in theconcentrated liquid was changed to volatile oxidation products having alow boiling point.

0.07 kg of the oxidation product remaining in electric furnace 38 (i.e.,lead monoxide) was charged into reaction vessel 42 provided withdistillation column 43 and a jacket (not shown) for circulating aheating medium, and 1.2 kg of phenol was introduced into reaction vessel42 from conduit 45, to thereby obtain a mixture. The obtained mixturewas heated to and maintained at 160° C. (as measured at the heatingmedium) for 6 hours under atmospheric pressure, thereby performing areaction. Then, the heating temperature was elevated to 200° C. (asmeasured at the heating medium) so as to cause both the water formed bythe reaction and unreacted phenol to be distilled off from the top ofdistillation column 43 through conduit 44, wherein the total amount ofthe water and the unreacted phenol both distilled off was 0.277 kg. Asample was taken from the reaction mixture remaining in reaction vessel42 and analyzed. The results of the analysis show that the remainingreaction mixture is a solution of lead(II) diphenoxide [Pb(OPh)₂] inphenol. 1 kg of the remaining reaction mixture was withdrawn fromreaction vessel 42 and transferred through conduit 46 and introducedinto storage vessel 47. Thereafter, every 100 hours after the point intime of 550 hours from the start of the operation (i.e., the point intime at which 1 kg of the concentrated liquid was withdrawn from storagevessel 36 and led into electric furnace 38 as mentioned above), asequence of the above operations using storage vessel 36 (from which 1kg of the concentrated liquid was withdrawn), electric furnace 38,reaction vessel 42 and storage vessel 47 (into which 1 kg of theremaining reaction mixture obtained in reaction vessel 42 wasintroduced) was repeated in the same manner as described above. On theother hand, from a point in time of 600 hours after the start of theoperation, the reaction mixture stored in storage vessel 47 wascontinuously withdrawn at a rate of 0.01 kg/hr through conduit 48, andthe reaction mixture withdrawn from storage vessel 47 was caused to meetthe evaporated gas which was withdrawn from thin-film evaporator 33 andwhich was led through conduit 35, and the resultant mixture (i.e., amixture of the products withdrawn through conduits 48 and 35) wasrecycled into the system for the transesterification through conduit 49.As mentioned above, the condensate withdrawal rate from condenser 22through conduit 23 during the period of time of from 400 hours to 600hours after the start of the operation was 32.99 kg/hr, and thecondensate withdrawal rate from condenser 22 through conduit 23 duringthe period of time of from 600 hours to 5,000 hours after the start ofthe operation was 33 kg/hr. During the period of time of from 400 hoursto 600 hours after the start of the operation, catalyst I was added todistillation column 1 through conduit 3 at such a feeding rate as tocompensate for the catalyst withdrawal rate at which the catalyst waswithdrawn through conduit 20, i.e., catalyst I was added through conduit3 at a feeding rate such that the above-mentioned Pb concentration of0.038% by weight in conduit 13 was able to be maintained. The operationwas conducted for 5,000 hours. From the point in time of 600 hours afterthe start of the operation, i.e., from the point in time at which therecycling of the catalyst into the system for the transesterificationthrough conduit 49 was started, there was no need for introducing afresh catalyst into the system for the transesterification. In addition,since the catalyst-containing liquid containing both the catalyst andhigh boiling point substances was withdrawn from the system for thetransesterification and subjected to the above-described treatmentsaccording to the present invention, a waste liquid containing a spentcatalyst did not occur at all. From the evaporation-concentrated liquidwhich was formed in evaporator 14 and which contained the catalyst andhigh boiling point substances, samples were taken through theabove-mentioned sampling nozzle provided on conduit 15′, wherein thesamples were, respectively, withdrawn at points in time of 1,000 hours,2,500 hours and 5,000 hours after the start of the operation. Thedetermination of the total concentration of the high boiling pointsubstances in each sample was conducted by the above-mentioned method.With respect to these samples withdrawn at points in time of 1,000hours, 2,500 hours and 5,000 hours after the start of the operation, thetotal concentrations of the high boiling point substances were 1.7% byweight, 1.8% by weight and 1.8% by weight, respectively.

During the 5,000 hour operation time, the operation could be stablyconducted (for example, both the flow and the composition in eachconduit were stable) without suffering disadvantageous phenomena, suchas the deposition of the catalyst from a catalyst-containing liquid andthe adherence of the deposited catalyst to the inside surfacesassociated with the equipment employed for the operation. During theoperation, samples of the reaction mixture withdrawn from the bottom ofcontinuous multi-stage distillation column 1 were taken through theabove-mentioned sampling nozzle provided on conduit 13, and the sampleswere analyzed. With respect to the reaction mixture which was taken fromconduit 13 at a point in time of 3,000 hours after the start of theoperation, the composition of the reaction mixture was as follows:phenol (PhOH): 31% by weight; methyl phenyl carbonate (MPC): 9% byweight; diphenyl carbonate (hereinafter, frequently referred to as“DPC”): 0.5% by weight; anisole (hereinafter, frequently referred to as“ANS”): 0.1% by weight; and Pb: 0.038% by weight. The purity of thearomatic carbonate (which was a mixture of MPC and DPC) in thecondensate withdrawn from condenser 22 through conduit 23 was 99.99% ormore, and no high boiling point substance was detected in thecondensate. After the operation was terminated, the inside surfacesassociated with the equipment employed for the operation were examined.No adherence of the catalyst to any of the inner walls of continuousmulti-stage distillation column 1, evaporator 14, reboiler 17, conduitsand the like was observed.

Comparative Example 1

Substantially the same procedure as in Example 1 was repeated, exceptthat the withdrawal of a portion of the evaporation-concentrated liquid(which was formed in evaporator 14 and which contained the catalyst andhigh boiling point substances) out of the production system throughconduit 20 was not conducted, and the introduction of the fresh catalystinto the system for the transesterification from conduit 3 throughpreheater 4 and conduit 5 into continuous multi-stage distillationcolumn 1 (which was conducted in Example 1 during the period of time offrom 400 hours to 600 hours after the start of the operation) was notconducted. With respect to the samples withdrawn at points in time of1,000 hours, 2,500 hours and 5,000 hours after the start of theoperation, the total concentrations of the high boiling point substanceswere 5.2% by weight, 14.6% by weight and 32.0% by weight, respectively.With respect to the reaction mixture which was taken from conduit 13 ata point in time of 3,000 hours after the start of the operation, thecomposition of the reaction mixture was as follows: PhOH: 33% by weight;MPC: 6.5% by weight; DPC: 0.2% by weight; ANS: 0.1% by weight; and Pb:0.038% by weight. The purity of the aromatic carbonate (which was amixture of MPC and DPC) in the condensate withdrawn from condenser 22through conduit 23 was 97%, and the total concentration of the highboiling point substances in the above-mentioned condensate was 1.5% byweight. After the operation was terminated (the operation was conductedfor 5,000 hours), the inside surfaces associated with the equipmentemployed for the operation were examined. The adherence of the catalystto a part of the inner wall of each of continuous multi-stagedistillation column 1, evaporator 14 and the conduits was observed.

Comparative Example 2

Substantially the same procedure as in Example 1 was repeated, exceptthat, after an evaporation-concentrated liquid containing the catalystand high boiling point substances was withdrawn from the bottom ofthin-film evaporator 33, the evaporation-concentrated liquid wasintroduced into and accumulated in a waste catalyst storage vessel (notshown) instead of leading the evaporation-concentrated liquid to storagevessel 36, so that the sequence of the operations using storage vessel36, electric furnace 38, reaction vessel 42 and storage vessel 47 wasnot conducted; and not only during the period of time of from 400 hoursto 600 hours after the start of the operation, but also after the pointin time of 600 hours after the start of the operation, catalyst I wasadded to distillation column 1 through conduit 3 at such a feeding rateas to compensate for the catalyst withdrawal rate at which the catalystwas withdrawn through conduit 20, i.e., catalyst I was added throughconduit 3 at a feeding rate such that the Pb concentration of 0.038% byweight in conduit 13 was able to be maintained. The operation wasconducted for 5,000 hours. During the period of time of from 600 hoursto 5,000 hours after the start of the operation, in order to maintainthe above-mentioned Pb concentration of 0.038% by weight in conduit 13,it was necessary to add fresh catalyst I to continuous multi-stagedistillation column 1 through conduit 3 in an amount as large as 2.86kg, in terms of the weight of Pb in the catalyst. During the period oftime of from 600 hours to 5,000 hours after the start of the operation,the amount of the evaporation-concentrated liquid (containing thecatalyst and high boiling point substances) which was withdrawn from thebottom of thin-film evaporator 33 and introduced into and accumulated inthe waste catalyst storage vessel reached a level as large as 44 kg.

EXAMPLE 2

The production of diphenyl carbonate (DPC) from methyl phenyl carbonate(MPC) was conducted using catalyst I prepared in Example 1, and thesystem as shown in FIG. 2, which comprises continuous multi-stagedistillation column 1 having a height of 6 m and a diameter of 4 inchesand equipped with 20 sieve trays.

A mixture of MPC and catalyst I was continuously fed in liquid form fromconduit 3 through preheater 4 and conduit 5 into continuous multi-stagedistillation column 1 at a position of 2.0 m below top 2 thereof at arate of 8 kg/hr, and was allowed to flow down inside multi-stagedistillation column 1, thereby performing a reaction. Catalyst I wasused in an amount such that the Pb concentration of the reaction mixturein conduit 13 became 0.19% by weight, wherein the Pb concentration canbe confirmed using a sample withdrawn through a sampling nozzle (notshown) provided on conduit 13.

The reaction conditions of the above reaction were such that thetemperature at the bottom of continuous multistage distillation column 1was 195° C. and the pressure at the top of continuous multi-stagedistillation column 1 was 2.59×10⁴ Pa. Gas distilled from top 2 ofcontinuous multi-stage distillation column 1 was led through conduit 25into condenser 26, in which the gas was condensed. A portion of theresultant condensate was recycled into top 2 of continuous multi-stagedistillation column 1 through conduits 27 and 28, and the remainder ofthe condensate was continuously withdrawn at a rate of 2.4 kg/hr throughconduits 27 and 29. A portion of the reaction mixture at bottom 6 ofcontinuous multi-stage distillation column 1 was led into reboiler 31through conduit 30, and recycled into column bottom 6 through conduit32, and the remainder of the reaction mixture was led into evaporator 14through conduit 13 at a rate of 7.6 kg/hr. From evaporator 14, anevaporated gas containing DPC was withdrawn and led through conduit 21into condenser 22, in which the gas was condensed. The resultantcondensate was withdrawn from condenser 22 through conduit 23 at a rateof 5.6 kg/hr. On the other hand, an evaporation-concentrated liquidcontaining the catalyst and high boiling point substances was formed inevaporator 14. A portion of the concentrated liquid was led intoreboiler 17 through conduits 15 and 16 and recycled into evaporator 14through conduit 18. The remainder of the concentrated liquid inevaporator 14 was recycled into continuous multi-stage distillationcolumn 1 through conduits 15, 19 and 3 at a rate of 2 kg/hr. After thestart of the recycling of the concentrated liquid into continuousmulti-stage distillation column 1 through conduits 15, 19 and 3, thefeeding rate of the mixture of MPC and catalyst I through conduit 3 intocontinuous multi-stage distillation column 1 was appropriatelycontrolled according to the recycling rate of the concentrated liquid.

During the period of time of from 400 hours to 5,000 hours after thestart of the operation, a portion of the concentrated liquid formed inevaporator 14 was continuously withdrawn through conduit 20 at a rate of0.05 kg/hr and led into thin-film evaporator 33. At a point in time of1,000 hours after the start of the operation, a sample (of theconcentrated liquid withdrawn from evaporator 14) was taken through asampling nozzle (not shown) provided on conduit 15′, and was analyzed todetermine the composition of the concentrated liquid by theabove-mentioned methods. The concentrated liquid had the followingcomposition: Pb (which is the metal component of catalyst I): 0.7% byweight; the total concentration of high boiling point substances: 5.0%by weight; and phenyl salicylate (which is a high boiling pointsubstance): 0.25% by weight. The evaporated gas formed in thin-filmevaporator 33 was continuously withdrawn therefrom through conduit 35 ata rate of 0.04 kg/hr and recycled through conduit 49 into the system forthe transesterification. On the other hand, an evaporation-concentratedliquid containing the catalyst and high boiling point substances wascontinuously withdrawn from the bottom of thin-film evaporator 33through conduit 34 at a rate of 0.01 kg/hr and led into storage vessel36. A sample (of the evaporation-concentrated liquid withdrawn fromthin-film evaporator 33) was taken through a sampling nozzle (not shown)provided on conduit 34 at a point in time of 1,000 hours after the startof the operation, and was analyzed to determine the composition of theevaporation-concentrated liquid by the above-mentioned methods. Theevaporation-concentrated liquid had the following composition: Pb (whichis the metal component of catalyst I): 3.5% by weight; the totalconcentration of high boiling point substances: 24.8% by weight; andphenyl salicylate (which is a high boiling point substance): 1.3% byweight.

At a point in time of 550 hours after the start of the operation, 1 kgof the concentrated liquid stored in storage vessel 36 was withdrawnthrough conduit 37 and led into reaction vessel 50 which had a capacityof 10 liters and which was provided with distillation column 54, ajacket (not shown) for circulating a heating medium, and an agitator.The temperature of reaction vessel 50 was elevated to 180° C. (asmeasured at the jacket). Then, both a feeding of carbon dioxide intoreaction vessel 50 at a flow rate of 3.9 NL/hr [NL means L (liter) asmeasured under the normal temperature and pressure conditions, namely at0° C. under 1 atm.] and a feeding of water into reaction vessel 50 at aflow rate of 3.1 g/hr were conducted for 2 hours while stirring, tothereby effect a reaction, thus obtaining a reaction mixture containinglead(II) carbonate as a reaction product. This reaction was conductedunder atmospheric pressure. After the lapse of the 2-hour reaction time,the stirring was stopped so as to allow the solids [containing thelead(II) carbonate] in the obtained reaction mixture to be precipitated.After the precipitation, the resultant supernatant in the reactionmixture was withdrawn through conduit 53. The concentration of Pb in thewithdrawn supernatant was 400 ppm by weight.

Then, 1.021 kg of PhOH was charged into reaction vessel 50 and stirredat 180° C. (as measured at the jacket) under atmospheric pressure, tothereby effect a reaction. During the reaction, unreacted PhOH wasdistilled off from the top of distillation column 54 disposed onreaction vessel 50 at a rate of 0.1 kg/hr through conduit 55A. Thus, inreaction vessel 50, a reaction proceeded in which lead(II) carbonatereacts with PhOH to form diphenoxy lead, carbon dioxide and water. Thecarbon dioxide and water formed in the above reaction were withdrawnfrom the reaction vessel together with the unreacted PhOH distilled off.A reaction mixture, which remained in reaction vessel 50 afterperforming the above reaction for 2 hours, was withdrawn from reactionvessel 50 and transferred through conduit 46 and introduced into storagevessel 47.

Thereafter, every 100 hours after the point in time of 550 hours fromthe start of the operation (i.e., the point in time at which 1 kg of theconcentrated liquid was withdrawn from storage vessel 36 and led intoreaction vessel 50 as mentioned above), a sequence of the aboveoperations using storage vessel 36 (from which 1 kg of the concentratedliquid was withdrawn), reaction vessel 50 and storage vessel 47 (intowhich the remaining reaction mixture obtained in reaction vessel 50 wasintroduced) was repeated in the same manner as described above. On theother hand, from a point in time of 600 hours after the start of theoperation, the reaction mixture stored in storage vessel 47 wascontinuously withdrawn at a rate of 0.01 kg/hr through conduit 48, andthe reaction mixture withdrawn from storage vessel 47 was caused to meetthe evaporated gas which was withdrawn from thin-film evaporator 33 andwhich was led through conduit 35, and the resultant mixture (i.e., amixture of the products withdrawn through conduits 48 and 35) wasrecycled into the system for the transesterification through conduit 49.The condensate withdrawal rate from condenser 22 through conduit 23during the period of time of from 400 hours to 600 hours after the startof the operation was 5.55 kg/hr, and the condensate withdrawal rate fromcondenser 22 through conduit 23 during the period of time of from 600hours to 5,000 hours after the start of the operation was 5.6 kg/hr.During the period of time of from 400 hours to 600 hours after the startof the operation, catalyst I was added to distillation column 1 throughconduit 3 at such a feeding rate as to compensate for the catalystwithdrawal rate at which the catalyst was withdrawn through conduit 20,i.e., catalyst I was added through conduit 3 at a feeding rate such thatthe above-mentioned Pb concentration of 0.19% by weight in conduit 13was able to be maintained.

The operation was conducted for 5,000 hours. From the point in time of600 hours after the start of the operation, i.e., from the point in timeat which the recycling of the catalyst into the system for thetransesterification through conduit 49 was started, the feeding rate ofcatalyst I into the system for the transesterification through conduit 3was as small as 0.0033 g/hr, in terms of the weight of Pb contained incatalyst I. Further, during the operation, the above-mentionedsupernatant (containing Pb) withdrawn from reaction vessel 50 throughconduit 53 was subjected to burning to thereby obtain lead monoxide andthe obtained lead monoxide was used for producing catalyst I. The amountof catalyst I which was prepared from the thus obtained lead monoxide(recovered Pb) was sufficient to be used as catalyst I which was to beintroduced in an amount as small as 0.0033 g/hr through conduit 3 (fromthe point in time of 600 hours after the start of the operation, i.e.,from the point in time at which the recycling of the catalyst into thesystem for the transesterification through conduit 49 was started).Therefore, from the point in time of 600 hours after the start of theoperation, all need for the catalyst was met by both the recycledcatalyst and the catalyst prepared from the Pb recovered from thesupernatant withdrawn from reaction vessel 50.

In addition, as mentioned above, the supernatant withdrawn from reactionvessel 50 was subjected to burning to obtain lead monoxide, and theobtained lead monoxide was recovered and used for preparing catalyst I.Therefore, a waste liquid containing a spent catalyst did not occur atall.

From the evaporation-concentrated liquid which was formed in evaporator14 and which contained the catalyst and high boiling point substances,samples were taken through a sampling nozzle provided on conduit 15′,wherein the samples were, respectively, withdrawn at points in time of1,000 hours, 2,500 hours and 5,000 hours after the start of theoperation. The determination of the total concentration of the highboiling point substances in each sample was conducted by theabove-mentioned method. With respect to these samples withdrawn atpoints in time of 1,000 hours, 2,500 hours and 5,000 hours after thestart of the operation, the total concentrations of the high boilingpoint substances were 5.0% by weight, 5.1% by weight and 5.1% by weight,respectively, and the phenyl salicylate concentrations were 0.25% byweight, 0.25% by weight and 0.26% by weight, respectively.

During the 5,000 hour operation time, the operation could be stablyconducted (for example, both the flow and the composition in eachconduit were stable) without suffering disadvantageous phenomena, suchas the deposition of the catalyst from a catalyst-containing liquid andthe adherence of the deposited catalyst to the inside surfacesassociated with the equipment employed for the operation. During theoperation, samples of the reaction mixture withdrawn from the bottom ofcontinuous multi-stage distillation column 1 were taken through theabove-mentioned sampling nozzle provided on conduit 13, and the sampleswere analyzed. With respect to the reaction mixture which was taken fromconduit 13 at a point in time of 3,000 hours after the start of theoperation, the composition of the reaction mixture was as follows: MPC:23.8% by weight; DPC: 74.6% by weight; and Pb: 0.19% by weight. Thepurity of the aromatic carbonate (which was a mixture of MPC and DPC) inthe condensate withdrawn from condenser 22 through conduit 23 was 99.99%or more, and no high boiling point substance was detected in thecondensate. After the operation was terminated, the inside surfacesassociated with the equipment employed for the operation were examined.No adherence of the catalyst to any of the inner walls of continuousmulti-stage distillation column 1, evaporator 14, reboiler 17, conduitsand the like was observed.

Comparative Example 3

Substantially the same procedure as in Example 2 was repeated, exceptthat, after an evaporation-concentrated liquid containing the catalystand high boiling point substances was withdrawn from the bottom ofthin-film evaporator 33, the evaporation-concentrated liquid wasintroduced into and accumulated in a waste catalyst storage vessel (notshown) instead of leading the evaporation-concentrated liquid to storagevessel 36, so that the sequence of the operations using storage vessel36, electric furnace 38, reaction vessel 42 and storage vessel 47 wasnot conducted; and not only during the period of time of from 400 hoursto 600 hours after the start of the operation, but also after the pointin time of 600 hours after the start of the operation, catalyst I wasadded to distillation column 1 through conduit 3 at such a feeding rateas to compensate for the catalyst withdrawal rate at which the catalystwas withdrawn through conduit 20, i.e., catalyst I was added throughconduit 3 at a feeding rate such that the Pb concentration of 0.19% byweight in conduit 13 was able to be maintained. The operation wasconducted for 5,000 hours. During the period of time of from 600 hoursto 5,000 hours after the start of the operation, in order to maintainthe above-mentioned Pb concentration of 0.19% by weight in conduit 13,it was necessary to add fresh catalyst I to continuous multi-stagedistillation column 1 through conduit 3 in an amount as large as 1.54kg, in terms of the weight of Pb in the catalyst. During the period oftime of from 600 hours to 5,000 hours after the start of the operation,the amount of the evaporation-concentrated liquid (containing thecatalyst and high boiling point substances) which was withdrawn from thebottom of thin-film evaporator 33 and introduced into and accumulated inthe waste catalyst storage vessel reached a level as large as 44 kg.

EXAMPLE 3

The production of diphenyl carbonate was conducted using catalyst Iprepared in Example 1, and the system as shown in FIG. 3.

A mixture of dimethyl carbonate, PhOH (which contains, as an impurity,200 ppm by weight of 4,4′-dihydroxydiphenyl which is a high boilingpoint substance) and methyl phenyl carbonate was continuously fed inliquid form from conduit 3 through preheater 4 and conduit 5 intocontinuous multi-stage distillation column 1 at a position of 0.5 mbelow the top 2 thereof (which column was comprised of a plate columnhaving a height of 12 m and a diameter of 8 inches and provided with 40sieve trays) at a rate of 31 kg/hr, thereby allowing the mixture to flowdown inside continuous multi-stage distillation column 1 so as toperform a reaction. The composition of the mixture fed from conduit 3was so controlled that the mixture flowing through conduit 5 during theoperation (the mixture flowing through conduit 5 was comprised of aliquid introduced from conduit 19, which was recycled from evaporator14; a liquid introduced from conduit 129, which was recycled fromcontinuous multi-stage distillation column 101; and the above-mentionedmixture fed from conduit 3) had a composition of 49.9% by weight of DMC,44.7% by weight of PhOH and 4.9% by weight of MPC. DMC was fed throughconduit 7 to evaporator 8, in which the DMC was subjected toevaporation. The resultant gas was fed to bottom 6 of continuousmulti-stage distillation column 1 through conduit 9 at a rate of 55kg/hr. Catalyst I was fed from conduit 224 in such an amount that the Pbconcentration at conduit 13 became 0.042% by weight, wherein the Pbconcentration can be confirmed using a sample withdrawn from a samplingnozzle (not shown) provided on conduit 13. Continuous multi-stagedistillation column 1 was operated under conditions such that thetemperature at the column bottom was 203° C. and the pressure at thecolumn top was 7.4×10⁵ Pa. Continuous multi-stage distillation column 1was clad with a heat insulating material and a part of the column washeated by a heater (not shown). Gas distilled from top 2 of the columnwas led through conduit 10 into condenser 11, in which the gas wascondensed. The resultant condensate was continuously withdrawn at a rateof 55 kg/hr from conduit 12. A reaction mixture was withdrawncontinuously from bottom 6 at a rate of 31 kg/hr, and was led toevaporator 14 through conduit 13. In evaporator 14, anevaporation-concentrated liquid containing the catalyst and high boilingpoint substances was formed. A portion of the concentrated liquid wasled into reboiler 17 through conduits 15 and 16 and recycled intoevaporator 14 through conduit 18. The remainder of the concentratedliquid in evaporator 14 was recycled into continuous multi-stagedistillation column 1 at a rate of 1 kg/hr through conduits 15, 19 and3. During the period of time from 400 hours to 5,000 hours after thestart of the operation, a portion of the concentrated liquid formed inevaporator 14 was continuously withdrawn from conduit 20 at a rate of0.05 kg/hr and introduced into thin-film evaporator 33.

Catalyst I was fed from conduit 224 at such a feeding rate as tocompensate for the catalyst withdrawal rate at which the catalyst waswithdrawn through conduit 20, i.e., catalyst I was fed from conduit 224at a feeding rate such that the above-mentioned Pb concentration of0.042% by weight in conduit 13 was able to be maintained. On the otherhand, an evaporated gas formed in evaporator 14 was fed through conduits21 and 105 into continuous multi-stage distillation column 101 at aposition of 2.0 m below top 102 thereof, which column was comprised of aplate column having a height of 6 m and a diameter of 10 inches andprovided with 20 sieve trays, thereby performing a reaction. Thecomposition of the mixture in conduit 105 was as follows: DMC: 43.1% byweight; PhOH: 24.5% by weight; MPC: 27.1% by weight; and DPC: 4.5% byweight (the mixture in conduit 105 was comprised of a gas introducedthrough conduit 21 and a liquid introduced from conduit 119, which wasrecycled from evaporator 114). Catalyst I was fed from conduit 124 insuch an amount that the Pb concentration at conduit 113 became 0.16% byweight, wherein the Pb concentration can be confirmed using a samplewithdrawn from a sampling nozzle (not shown) provided on conduit 113.Continuous multi-stage distillation column 101 was operated underconditions such that the temperature at the column bottom was 198° C.and the pressure at the column top was 3.7×10⁴ Pa. Gas distilled fromcolumn top 102 was led through conduit 125 to condenser 126, in whichthe gas was condensed. A portion of the resultant condensate wasrecycled into column top 102 through conduit 128, and the remainder ofthe condensate was recycled into continuous multi-stage distillationcolumn 1 through conduits 127 and 129, preheater 4 and conduit 5. Afterthe start of the recycling of the condensate into continuous multi-stagedistillation column 1 through conduit 129, PhOH (containing 200 ppm byweight of 4,4′-dihydroxydiphenyl which is a high boiling pointsubstance) was added to the mixture fed from conduit 3 in such an amountthat the above-mentioned composition of the mixture at conduit 5 can bemaintained. A portion of the reaction mixture at bottom 106 ofcontinuous multi-stage distillation column 101 was led into reboiler 131through conduit 130, and recycled into column bottom 106 through conduit132, and the remainder of the reaction mixture was led to evaporator 114through conduit 113 at a rate of 8.8 kg/hr. In evaporator 114, anevaporation-concentrated liquid containing the catalyst and high boilingpoint substances was formed. A portion of the concentrated liquid wasled into reboiler 117 through conduits 115 and 116 and recycled intoevaporator 114 through conduit 118. The remainder of the concentratedliquid in evaporator 114 was recycled into continuous multi-stagedistillation column 101 through conduits 115, 119 and 105 at a rate of 2kg/hr. During the period of time of from 400 hours to 5,000 hours afterthe start of the operation, a portion of the concentrated liquid formedin evaporator 114 was continuously withdrawn at a rate of 0.05 kg/hrfrom the system for the transesterification through conduit 120, and wascaused to meet the concentrated liquid led through conduit 20. Theresultant liquid mixture (i.e., a mixture of the liquid productswithdrawn from the system for the transesterification through conduits120 and 20) was led into thin-film evaporator 33 through conduit 20′. Ata point in time of 1,000 hours after the start of the operation, asample (of the above-mentioned liquid mixture) was taken through asampling nozzle (not shown) provided on conduit 20′, and was analyzed todetermine the composition of the liquid mixture by the above-mentionedmethods. The liquid mixture had the following composition: Pb (which isthe metal component of catalyst I): 1.0% by weight; the totalconcentration of high boiling point substances: 3.3% by weight;4,4′-dihydroxydiphenyl (which is a high boiling point substance): 1.8%by weight; and phenyl salicylate: 0.13% by weight. The evaporated gasformed in thin-film evaporator 33 was continuously withdrawn therefromthrough conduit 35 at a rate of 0.09 kg/hr and recycled through conduit149 into the system for the transesterification. On the other hand, anevaporation-concentrated liquid containing the catalyst and high boilingpoint substances was continuously withdrawn from the bottom of thin-filmevaporator 33 through conduit 34 at a rate of 0.01 kg/hr and led intostorage vessel 36. A sample (of the evaporation-concentrated liquidwithdrawn from thin-film evaporator 33) was taken through a samplingnozzle (not shown) provided on conduit 34 at a point in time of 1,000hours after the start of the operation, and was analyzed to determinethe composition of the evaporation-concentrated liquid by theabove-mentioned methods. The evaporation-concentrated liquid had thefollowing composition: Pb (which is the metal component of catalyst I):9.9% by weight; the total concentration of high boiling pointsubstances: 33.4% by weight; 4,4′-dihydroxydiphenyl (which is a highboiling point substance): 3.7% by weight; and phenyl salicylate: 1.3% byweight.

At a point in time of 550 hours after the start of the operation, 1 kgof the concentrated liquid stored in storage vessel 36 was withdrawnthrough conduit 37 and led into reaction vessel 50 which had a capacityof 10 liters and which was provided with distillation column 54, ajacket (not shown) for circulating a heating medium, and an agitator.The temperature of reaction vessel 50 was elevated to 180° C. (asmeasured at the jacket). Then, both a feeding of carbon dioxide intoreaction vessel 50 at a flow rate of 11 NL/hr and a feeding of waterinto reaction vessel 50 at a flow rate of 8.7 g/hr were conducted for 2hours while stirring, to thereby effect a reaction, thus obtaining areaction mixture containing lead(II) carbonate as a reaction product.This reaction was conducted under atmospheric pressure. After the lapseof the 2-hour reaction time, the stirring was stopped so as to allow thesolids [containing the lead(II) carbonate] in the obtained reactionmixture to be precipitated. After the precipitation, the resultantsupernatant in the reaction mixture was withdrawn through conduit 53.The concentration of Pb in the withdrawn supernatant was 400 ppm byweight.

Then, 0.620 kg of PhOH was charged into reaction vessel 50 and stirredat 180° C. (as measured at the jacket) under atmospheric pressure, tothereby effect a reaction. During the reaction, unreacted PhOH wasdistilled off from the top of distillation column 54 disposed onreaction vessel 50 at a rate of 0.1 kg/hr through conduit 55A. Thus, inreaction vessel 50, in the same manner as in Example 2, a reactionproceeded in which lead(II) carbonate reacts with PhOH to form diphenoxylead, carbon dioxide and water. The carbon dioxide and water formed inthe above reaction were withdrawn from the reaction vessel together withthe unreacted PhOH distilled off. A reaction mixture, which remained inreaction vessel 50 after performing the above reaction for 2 hours, waswithdrawn from reaction vessel 50 and transferred through conduit 46 andintroduced into storage vessel 47.

Thereafter, every 100 hours after the point in time of 550 hours fromthe start of the operation (i.e., the point in time at which 1 kg of theconcentrated liquid was withdrawn from storage vessel 36 and led intoreaction vessel 50 as mentioned above), a sequence of the aboveoperations using storage vessel 36 (from which 1 kg of the concentratedliquid was withdrawn), reaction vessel 50 and storage vessel 47 (intowhich the remaining reaction mixture obtained in reaction vessel 50 wasintroduced) was repeated in the same manner as described above. On theother hand, from a point in time of 600 hours after the start of theoperation, the reaction mixture stored in storage vessel 47 wascontinuously withdrawn at a rate of 0.01 kg/hr through conduit 48. Aportion of the reaction mixture withdrawn from storage vessel 47 wasrecycled into the system for the transesterification through conduit 49at a rate of 0.0065 kg/hr. The remainder of the reaction mixturewithdrawn from storage vessel 47 was led through conduit 48′ at a rateof 0.0035 kg/hr and caused to meet the evaporated gas which waswithdrawn from thin-film evaporator 33 and which was led through conduit35, and the resultant mixture (i.e., a mixture of the products withdrawnthrough conduits 48′and 35) was recycled into the system for thetransesterification through conduit 149.

During the period of time of from 400 hours to 600 hours after the startof the operation, catalyst I was added to distillation column 1 throughconduit 224 and to distillation column 101 through conduit 124 both atsuch a feeding rate as to compensate for the catalyst withdrawal rate atwhich the catalyst was withdrawn through conduits 20 and 120, i.e.,catalyst I was added through conduits 224 and 124 both at a feeding ratesuch that both of the above-mentioned Pb concentration of 0.042% byweight in conduit 13 and the above-mentioned Pb concentration of 0.16%by weight in conduit 113 were able to be maintained. An evaporated gasformed in evaporator 114 was fed through conduit 121 into continuousmulti-stage distillation column 201 at a position of 2.0 m below top 202thereof, which column was comprised of a plate column having a height of6 m and a diameter of 6 inches and provided with 20 sieve trays, therebyseparating DPC from the fed gas. Continuous multi-stage distillationcolumn 201 was operated under conditions such that the temperature atthe column bottom was 184° C. and the pressure at the column and top was2×10³ Pa. Gas distilled from top 202 of the column was led throughconduit 225 to condenser 226, in which the gas was condensed. A portionof the resultant condensate was recycled into top 202 of the columnthrough conduit 228, and the remainder of the condensate was recycledinto continuous multi-stage distillation column 101 through conduits 227and 229. A gas was withdrawn from continuous multi-stage distillationcolumn 201 through conduit 233 provided at a position of 4.0 m belowcolumn top 202 and was led to condenser 234, in which the withdrawn gaswas condensed. The resultant condensate was withdrawn at a rate of 6.7kg/hr through conduit 235.

The operation was conducted for 5,000 hours. From the point in time of600 hours after the start of the operation, i.e., from the point in timeat which the recycling of the catalyst into the system for thetransesterification through conduits 49 and 149 was started, the totalfeeding rate of catalyst I into the system for the transesterificationthrough conduits 124 and 224 was as small as 0.0032 g/hr, in terms ofthe weight of Pb contained in catalyst I. Further, during the operation,the above-mentioned supernatant (containing Pb) withdrawn from reactionvessel 50 through conduit 53 was subjected to burning to thereby obtainlead monoxide and the obtained lead monoxide was used for producingcatalyst I. The amount of catalyst I which was prepared from the thusobtained lead monoxide (recovered Pb) was sufficient to be used ascatalyst I which was to be introduced in the above-mentioned amount of0.0032 g/hr through conduits 124 and 224 (from the point in time of 600hours after the start of the operation, i.e., from the point in time atwhich the recycling of the catalyst into the system for thetransesterification through conduits 49 and 149 was started). Therefore,from the point in time of 600 hours after the start of the operation,all need for the catalyst was met by both the recycled catalyst and thecatalyst prepared from the Pb recovered from the supernatant withdrawnfrom reaction vessel 50.

In addition, as mentioned above, the supernatant withdrawn from reactionvessel 50 was subjected to burning to obtain lead monoxide, and theobtained lead monoxide was recovered and used for preparing catalyst I.Therefore, a waste liquid containing a spent catalyst did not occur atall.

From the evaporation-concentrated liquid which was formed in evaporator14 and which contained the catalyst and high boiling point substances,samples were taken through a sampling nozzle provided on conduit 15′,wherein the samples were, respectively, withdrawn at points in time of1,000 hours, 2,500 hours and 5,000 hours after the start of theoperation. The determination of the total concentration of the highboiling point substances in each sample was conducted by theabove-mentioned method. With respect to these samples withdrawn atpoints in time of 1,000 hours, 2,500 hours and 5,000 hours after thestart of the operation, the total concentrations of the high boilingpoint substances were 2.2% by weight, 2.3% by weight and 2.3% by weight,respectively. Further, from the evaporation-concentrated liquid whichwas formed in evaporator 114 and which contained the catalyst and highboiling point substances, samples were taken through a sampling nozzleprovided on conduit 115′, wherein the samples were, respectively,withdrawn at points in time of 1,000 hours, 2,500 hours and 5,000 hoursafter the start of the operation. With respect to these sampleswithdrawn at points in time of 1,000 hours, 2,500 hours and 5,000 hoursafter the start of the operation, the total concentrations of the highboiling point substances were 5.0% by weight, 5.1% by weight and 5.1% byweight, respectively, and the phenyl salicylate concentrations were0.25% by weight, 0.26% by weight and 0.26% by weight, respectively.

During the 5,000 hour operation time, the operation could be stablyconducted (for example, both the flow and the composition in eachconduit were stable) without suffering disadvantageous phenomena, suchas the deposition of the catalyst from a catalyst-containing liquid andthe adherence of the deposited catalyst to the inside surfacesassociated with the equipment employed for the operation. At a point intime of 3,000 hours after the start of the operation, the purity of thearomatic carbonate (which was DPC) in the condensate withdrawn fromcondenser 234 through conduit 235 was 99.99% or more, and no substanceother than DPC was detected in the condensate. After the operation wasterminated, the inside surfaces associated with the equipment employedfor the operation were examined. No adherence of the catalyst to any ofthe inner walls of continuous multi-stage distillation column 1,evaporator 14, reboiler 17, conduits and the like was observed.

Comparative Example 4

Substantially the same procedure as in Example 3 was repeated, exceptthat, with respect to the evaporation-concentrated liquid (containingthe catalyst and high boiling point substances) which was formed inevaporator 14 and the evaporation-concentrated liquid (containing thecatalyst and high boiling point substances) which was formed inevaporator 114, the withdrawal of a portion of each of theseevaporation-concentrated liquids out of the production system throughconduits 20 and 120 was not conducted, and that the introduction of thefresh catalyst into the system for the transesterification from conduits224 and 124 into continuous multi-stage distillation columns 1 and 101(which was conducted in Example 3 during the period of time of from 400hours to 5,000 hours after the start of the operation) was notconducted. With respect to the samples withdrawn through the samplingnozzle provided on conduit 115′ at points in time of 1,000 hours, 2,500hours and 5,000 hours after the start of the operation, the totalconcentrations of the high boiling point substances were 12.5% byweight, 30.4% by weight and 52.3% by weight, respectively, and thephenyl salicylate concentrations were 0.62% by weight, 1.7% by weightand 2.9% by weight, respectively.

With respect to the aromatic carbonate (which was DPC) in the condensatewithdrawn from condenser 234 through conduit 235 at a point in time of3,000 hours after the start of the operation, the purity thereof was98.7%. Further, the concentration of phenyl salicylate in theabove-mentioned condensate was 12 ppm by weight, and the totalconcentration of the high boiling point substances in theabove-mentioned condensate was 0.06% by weight. The operation wasconducted for 5,000 hours. After the operation was terminated, theinside surfaces associated with the equipment employed for the operationwere examined. The adherence of the catalyst to a part of the inner wallof each of continuous multi-stage distillation column 1, evaporator 14and the conduits was observed.

EXAMPLE 4

The production of an aromatic carbonate was conducted in substantiallythe same manner as in Example 2, except that the system as shown in FIG.4 was used instead of the system as shown in FIG. 2. As shown in FIGS. 4and 2, the difference between the system as shown in FIG. 4 and thesystem as shown in FIG. 2 resides in the region into which theconcentrated liquid stored in storage vessel 36 is introduced throughconduit 37 and from which a reaction mixture obtained from the aboveconcentrated liquid is transferred to storage vessel 47 through conduit46.

During the period of time of 400 hours to 5,000 hours after the start ofthe operation, a portion of the concentrated liquid formed in evaporator14 was continuously withdrawn through conduit 20 at a rate of 0.05 kg/hrand led into thin-film evaporator 33. At a point in time of 1,000 hoursafter the start of the operation, a sample (of the concentrated liquidwithdrawn from evaporator 14) was taken through a sampling nozzle (notshown) provided on conduit 15′, and was analyzed to determine thecomposition of the concentrated liquid by the above-mentioned methods.The concentrated liquid had the following composition: Pb (which is themetal component of catalyst I): 0.7% by weight; the total concentrationof high boiling point substances: 4.0% by weight; and phenyl salicylate(which is a high boiling point substance): 0.15% by weight. Theevaporated gas formed in thin-film evaporator 33 was continuouslywithdrawn therefrom through conduit 35 at a rate of 0.04 kg/hr andrecycled through conduit 49 into the system for the transesterification.On the other hand, an evaporation-concentrated liquid containing thecatalyst and high boiling point substances was continuously withdrawnfrom the bottom of thin-film evaporator 33 through conduit 34 at a rateof 0.01 kg/hr and led into storage vessel 36. A sample (of theevaporation-concentrated liquid withdrawn from thin-film evaporator 33)was taken through a sampling nozzle (not shown) provided on conduit 34at a point in time of 1,000 hours after the start of the operation, andwas analyzed to determine the composition of theevaporation-concentrated liquid by the above-mentioned methods. Theevaporation-concentrated liquid had the following composition: Pb (whichis the metal component of catalyst I): 3.5% by weight; the totalconcentration of high boiling point substances: 19.8% by weight; andphenyl salicylate (which is a high boiling point substance): 0.75% byweight.

At a point in time of 550 hours after the start of the reaction, 1 kg ofthe concentrated liquid stored in storage vessel 36 was withdrawnthrough conduit 37 and led into reaction vessel 55 which had a capacityof 10 liters and which was provided with distillation column 62, ajacket (not shown) for circulating a heating medium, and an agitator. 5kg of water was introduced into reaction vessel 55, and the temperatureof reaction vessel 55 was elevated to and maintained at 200° C. (asmeasured at the jacket) while stirring. The internal pressure ofreaction vessel 55 rose to 3.0×10⁶ Pa. After continuing the stirring at200° C. for 4 hours, the stirring was stopped, and the temperature ofreaction vessel 55 (as measured at the jacket) was lowered to 100° C.and allowed to stand for 1 hour. The internal pressure of reactionvessel 55 was lowered to atmospheric pressure by discharging gas fromreaction vessel 55 through conduit 63. From the resultant reactionmixture in reaction vessel 55, a liquid phase was withdrawn and led tostorage vessel 59 through conduit 58, leaving a white precipitate inreaction vessel 55. The white precipitate left in reaction vessel 55 wasanalyzed, and the results of the analysis showed that the whiteprecipitate was a solid comprised mainly of lead(II) carbonate. On theother hand, when the liquid phase introduced into storage vessel 59 wasallowed to cool to room temperature, it was separated into upper andlower liquid layers. The upper layer had the following composition:water: 93.5% by weight; PhOH: 6.5% by weight; and no high boiling pointsubstance was detected. The lower layer had the following composition:PhOH: 57.3% by weight; the total concentration of high boiling pointsubstances: 14.3% by weight; Pb: 100 ppm by weight; and phenylsalicylate was not detected at all. From the mass balance of PhOH,phenyl salicylate and high boiling point substances, it was found thatphenyl salicylate had been converted into PhOH by hydrolysis anddecarboxylation. The lower layer in storage vessel 59 was withdrawntherefrom through conduit 60. The weight of the lower layer withdrawnfrom storage vessel 59 was 603 g. The lead(II) carbonate in reactionvessel 55 was converted into diphenoxy lead in substantially the samemanner as in Example 2, i.e., by a method in which PhOH is introducedinto reaction vessel 55 through conduits 56 and 59A, and the resultantmixture in reaction vessel 55 is subjected to a reaction while stirringat 180° C. (as measured at the jacket) and distilling off by-producedwater and carbon dioxide together with unreacted PhOH. 1 kg of areaction mixture, which remained in reaction vessel 55 after performingthe above reaction for 2 hours, was withdrawn from reaction vessel 55and transferred through conduit 46 and introduced into storage vessel47.

Thereafter, every 100 hours after the point in time of 550 hours fromthe start of the operation (i.e., the point in time at which 1 kg of theconcentrated liquid was withdrawn from storage vessel 36 and led intoreaction vessel 55 as mentioned above), a sequence of the aboveoperations using storage vessel 36 (from which 1 kg of the concentratedliquid was withdrawn), reaction vessel 55, storage vessel 59 and storagevessel 47 (into which 1 kg of the remaining reaction mixture obtained inreaction vessel 55 was introduced) was repeated in the same manner asdescribed above. With respect to each of the second-time to last-timepractices of the above-mentioned sequence of the operations usingstorage vessel 36, reaction vessel 55, storage vessel 59 and storagevessel 47, as the 5 kg of water which is introduced into reaction vessel55 (so as to be mixed with 1 kg of the concentrated liquid transferredfrom storage vessel 36), use was made of an aqueous mixture obtained bya method in which the above-mentioned upper layer obtained in storagevessel 59 is taken out and water is added thereto in an amount such thatthe weight of the resultant aqueous mixture becomes 5 kg.

On the other hand, from a point in time of 600 hours after the start ofthe operation, the reaction mixture stored in storage vessel 47 wascontinuously withdrawn at a rate of 0.01 kg/hr through conduit 48, andthe reaction mixture withdrawn from storage vessel 47 was caused to meetthe evaporated gas which was withdrawn from thin-film evaporator 33 andwhich was led through conduit 35, and the resultant mixture (i.e., amixture of the products withdrawn through conduits 48 and 35) wasrecycled into the system for the transesterification through conduit 49.

The condensate withdrawal rate from condenser 22 through conduit 23during the period of time of from 400 hours to 600 hours after the startof the operation was 5.55 kg/hr, and the condensate withdrawal rate fromcondenser 22 through conduit 23 during the period of time of from 600hours to 5,000 hours after the start of the operation was 5.6 kg/hr.During the period of time of from 400 hours to 600 hours after the startof the operation, catalyst I was added to distillation column 1 throughconduit 3 at such a feeding rate as to compensate for the catalystwithdrawal rate at which the catalyst was withdrawn through conduit 20,i.e., catalyst I was added through conduit 3 at a feeding rate such thatthe Pb concentration of 0.19% by weight in conduit 13 was able to bemaintained.

The operation was conducted for 5,000 hours. From the point in time of600 hours after the start of the operation, i.e., from the point in timeat which the recycling of the catalyst into the system for thetransesterification through conduit 49 was started, the feeding rate ofcatalyst I into the system for the transesterification through conduit 3was as small as 0.0006 g/hr, in terms of the weight of Pb contained incatalyst I. Further, during the operation, the above-mentioned lowerlayer (containing Pb) withdrawn from storage vessel 59 through conduit60 was subjected to burning to thereby obtain lead monoxide and theobtained lead monoxide was used for producing catalyst I. The amount ofcatalyst I which was prepared from the thus obtained lead monoxide(recovered Pb) was sufficient to be used as catalyst I which was to beintroduced in an amount as small as 0.0006 g/hr through conduit 3 (fromthe point in time of 600 hours after the start of the operation, i.e.,from the point in time at which the recycling of the catalyst into thesystem for the transesterification through conduit 49 was started).Therefore, from the point in time of 600 hours after the start of theoperation, all need for the catalyst was met by both the recycledcatalyst and the catalyst prepared from the Pb recovered from the lowerlayer withdrawn from storage vessel 59 (wherein the lower layerwithdrawn from storage vessel 59 is a portion of the liquid phasewithdrawn from reaction vessel 55).

In addition, as mentioned above, the lower layer withdrawn from storagevessel 59 through conduit 60 was subjected to burning to obtain leadmonoxide, and the obtained lead monoxide was recovered and used forpreparing catalyst I. Therefore, a waste liquid containing a spentcatalyst did not occur at all.

From the evaporation-concentrated liquid which was formed in evaporator14 and which contained the catalyst and high boiling point substances,samples were taken through a sampling nozzle provided on conduit 15′,wherein the samples were, respectively, withdrawn at points in time of1,000 hours, 2,500 hours and 5,000 hours after the start of theoperation. The determination of the total concentration of the highboiling point substances in each sample was conducted by theabove-mentioned method. With respect to these samples withdrawn atpoints in time of 1,000 hours, 2,500 hours and 5,000 hours after thestart of the operation, the total concentrations of the high boilingpoint substances were 4.0% by weight, 4.1% by weight and 4.1% by weight,respectively.

During the 5,000 hour operation time, the operation could be stablyconducted (for example, both the flow and the composition in eachconduit were stable) without suffering disadvantageous phenomena, suchas the deposition of the catalyst from a catalyst-containing liquid andthe adherence of the deposited catalyst to the inside surfacesassociated with the equipment employed for the operation. During theoperation, samples of the reaction mixture withdrawn from the bottom ofcontinuous multi-stage distillation column 1 were taken through thesampling nozzle provided on conduit 13, and the samples were analyzed.With respect to the reaction mixture which was taken from conduit 13 ata point in time of 3,000 hours after the start of the operation, thecomposition of the reaction mixture was as follows: MPC: 23.9% byweight; DPC: 74.8% by weight; and Pb: 0.19% by weight. The purity of thearomatic carbonate (which was a mixture of MPC and DPC) in thecondensate withdrawn from condenser 22 through conduit 23 was 99.99% ormore, and no high boiling point substance was detected in thecondensate. After the operation was terminated, the inside surfacesassociated with the equipment employed for the operation were examined.No adherence of the catalyst to any of the inner walls of continuousmulti-stage distillation column 1, evaporator 14, reboiler 17, conduitsand the like was observed.

EXAMPLE 5 Preparation of Catalyst

A mixture of 30 kg of PhOH, 10 kg of methyl phenyl carbonate and 8 kg ofdibutyltin oxide was heated to and maintained at 180° C. for 10 hours,there-by performing a reaction. After that period of time, water formedin the resultant reaction mixture was distilled off together withunreacted PhOH. Then, most of the remaining PhOH and methyl phenylcarbonate were distilled off from the reaction mixture under reducedpressure, and the resultant mixture was allowed to cool in a nitrogenatmosphere, to thereby obtain catalyst II.

Production of Aromatic Carbonate

The production of an aromatic carbonate was conducted using the systemas shown in FIG. 5, which comprises distillation column 24 having aheight of 1 m and a diameter of 4 inches and containing Dixon packing (6mmφ), and reaction vessel 100 having a capacity of 200 liters andequipped with an agitator.

A mixture of dimethyl carbonate, PhOH and catalyst II was continuouslyfed in liquid form from conduit 3 into reaction vessel 100 at a rate of20 kg/hr, thereby performing a reaction. The weight ratio of thedimethyl carbonate to the PhOH in the mixture was 50/50, and catalyst IIwas used in an amount such that the Sn concentration of the reactionmixture in conduit 13 became 0.4% by weight, wherein the Snconcentration can be confirmed using a sample withdrawn through asampling nozzle (not shown) provided on conduit 13. The reactionconditions of the above reaction were such that the temperature inreaction vessel 100 was 204° C. and the pressure at the top ofdistillation column 24 was 7.5×10⁵ Pa. Gas (containing methanol anddimethyl carbonate) formed in reaction vessel 100 was led intodistillation column 24 through conduit 30. From distillation column 24,dimethyl carbonate was recycled to reaction vessel 100 through conduit32, while the gas (containing methanol and dimethyl carbonate) distilledfrom the top of distillation column 24 was led through conduit 25 intocondenser 26, in which the gas was condensed. A portion of the resultantcondensate was recycled into distillation column 24 at a reflux ratio of5.0 through conduits 27 and 28, and the remainder of the condensate wascontinuously withdrawn at a rate of 2.3 kg/hr through conduit 29. Areaction mixture [containing methyl phenyl carbonate (as a desiredreaction product), the catalyst, and high boiling point substances] wascontinuously withdrawn from the bottom of reaction vessel 100 at a rateof 17.7 kg/hr through conduit 13 and led into evaporator 14, from whichan evaporated gas containing the methyl phenyl carbonate was withdrawnand led through conduit 21 into condenser 22, in which the evaporatedgas was condensed. The resultant condensate was withdrawn from condenser22 through conduit 23 at a rate of 16.7 kg/hr. On the other hand, anevaporation-concentrated liquid containing the catalyst and the highboiling point substances was formed in evaporator 14. A portion of theconcentrated liquid was led into reboiler 17 through conduits 15 and 16and recycled into evaporator 14 through conduit 18. The remainder of theconcentrated liquid in evaporator 14 was recycled into reaction vessel100 at a rate of 1 kg/hr through conduits 15, 19 and 3. During theperiod of time of from 400 hours to 2,000 hours after the start of theoperation, a portion of the concentrated liquid formed in evaporator 14was continuously withdrawn through conduit 20 at a rate of 0.05 kg/hrand led into storage vessel 36 having a capacity of 10 liters. At apoint in time of 1,000 hours after the start of the operation, a sample(of the concentrated liquid withdrawn from evaporator 14) was takenthrough a sampling nozzle (not shown) provided on conduit 15′, and wasanalyzed to determine the composition of the concentrated liquid by theabove-mentioned methods. The concentrated liquid had the followingcomposition: Sn (which is the metal component of catalyst II): 6.7% byweight; the total concentration of high boiling point substances: 2.2%by weight; and phenyl salicylate (which is a high boiling pointsubstance): 0.7% by weight.

At a point in time of 500 hours after the start of the operation, 2 kgof the concentrated liquid stored in storage vessel 36 was withdrawnthrough conduit 37 and led into reaction vessel 55 which had a capacityof 10 liters and which was equipped with distillation column 62, ajacket (not shown) for circulating a heating medium, and an agitator. 4kg of dimethyl carbonate was introduced into reaction vessel 55 fromconduit 56, and the temperature of reaction vessel 55 was elevated toand maintained at 200° C. (as measured at the jacket) while stirring.The pressure in reaction vessel 55 rose to 7.2×10⁵ Pa. After continuingthe stirring at 200° C. for 4 hours, the temperature of reaction vessel55 (as measured at the jacket) was lowered to 80° C. Then, thecomposition of the resultant reaction mixture in reaction vessel 55 wasanalyzed. The analysis of the composition showed that phenyl salicylatewas not present at all and, instead, methyl salicylate was present(wherein the methyl salicylate is presumed to have been formed by thereaction of phenyl salicylate with dimethyl carbonate). Thereafter,distillation was started by elevating the temperature of reaction vessel55 to 200° C. (as measured at the jacket) under atmospheric pressure,and a distillate begun to come out through conduit 63. The distillationwas continued while gradually lowering the pressure in reaction vessel55 from atmospheric pressure to reduced pressure. When the amount of thedistillate obtained through conduit 63 became 4.32 kg, the distillationwas terminated. Subsequently, the pressure in reaction vessel 55 wasadjusted to atmospheric pressure by introducing nitrogen gas, and theweight of the reaction mixture in reaction vessel 55 was adjusted to 2kg by introducing PhOH. The reaction mixture, which remained in reactionvessel 55 after performing the above distillation, was withdrawn fromreaction vessel 55 and transferred through conduit 46 and introducedinto storage vessel 47 having a capacity of 10 liters. The compositionof the reaction mixture was analyzed. The analysis of the compositionshowed that phenyl salicylate was not present at all and the totalconcentration of high boiling point substances had decreased to 0.8% byweight.

Thereafter, every 40 hours after the point in time of 500 hours from thestart of the operation (i.e., the point in time at which 2 kg of theconcentrated liquid was withdrawn from storage vessel 36 and led intoreaction vessel 55 as mentioned above), a sequence of the aboveoperations using storage vessel 36 (from which 2 kg of the concentratedliquid was withdrawn), reaction vessel 55 and storage vessel 47 (intowhich the remaining reaction mixture obtained in reaction vessel 55 wasintroduced) was repeated in the same manner as described above.

On the other hand, from a point in time of 600 hours after the start ofthe operation, the reaction mixture stored in storage vessel 47 wascontinuously withdrawn at a rate of 0.05 kg/hr through conduit 48 andrecycled into the system for the transesterification through conduit 49.

The condensate withdrawal rate from condenser 22 through conduit 23during the period of time of from 400 hours to 600 hours after the startof the operation was 16.65 kg/hr, and the condensate withdrawal ratefrom condenser 22 through conduit 23 during the period of time of from600 hours to 2,000 hours after the start of the operation was 16.7kg/hr. During the period of time of from 400 hours to 600 hours afterthe start of the operation, catalyst II was added to reaction vessel 100through conduit 3 at such a feeding rate as to compensate for thecatalyst withdrawal rate at which the catalyst was withdrawn throughconduit 20, i.e., catalyst II was added through conduit 3 at a feedingrate such that the above-mentioned Sn concentration of 0.4% by weight inconduit 13 was able to be maintained.

The operation was carried out for 2,000 hours. From the period of timeof from 600 hours after the start of the operation, i.e., from the pointin time at which the recycling of the catalyst into the system for thetransesterification through conduit 49 was started, there was no needfor introducing a fresh catalyst into the system for thetransesterification. In addition, since the catalyst-containing liquidcontaining both the catalyst and high boiling point substances waswithdrawn from the system for the transesterification and subjected tothe above-described treatments according to the present invention, awaste liquid containing a spent catalyst did not occur at all.

From the evaporation-concentrated liquid which was formed in evaporator14 and which contained the catalyst and high boiling point substances,samples were taken through the above-mentioned sampling nozzle providedon conduit 15′, wherein the samples were, respectively, withdrawn atpoints in time of 1,000 hours, 1,500 hours and 2,000 hours after thestart of the operation. The determination of the total concentration ofthe high boiling point substances in each sample was conducted by theabove-mentioned method. With respect to these samples withdrawn atpoints in time of 1,000 hours, 1,500 hours and 2,000 hours after thestart of the operation, the total concentrations of the high boilingpoint substances were 2.2% by weight, 2.2% by weight and 2.2% by weight,respectively.

During the 2,000 hour operation time, the operation could be stablyconducted (for example, both the flow and the composition in eachconduit were stable) without suffering disadvantageous phenomena, suchas the deposition of the catalyst from a catalyst-containing liquid andthe adherence of the deposited catalyst to the inside surfacesassociated with the equipment employed for the operation. During theoperation, samples of the reaction mixture withdrawn from the bottom ofreaction vessel 100 were taken through the above-mentioned samplingnozzle provided on conduit 13, and the samples were analyzed. Withrespect to the reaction mixture which was taken from conduit 13 at apoint in time of 2,000 hours after the start of the operation, thecomposition of the reaction mixture was as follows: PhOH: 51% by weight;methyl phenyl carbonate (MPC): 6% by weight; diphenyl carbonate (DPC):0.4% by weight; anisole (ANS): 0.6% by weight; and Sn: 0.4% by weight.The purity of the aromatic carbonate (which was a mixture of MPC andDPC) in the condensate withdrawn from condenser 22 through conduit 23was 99.99% or more, and no high boiling point substance was detected inthe condensate. After the operation was terminated, the inside surfacesassociated with the equipment employed for the operation were examined.No adherence of the catalyst to any of the inner walls of reactionvessel 100, evaporator 14, reboiler 17, conduits and the like wasobserved.

EXAMPLE 6 Preparation of Catalyst

A mixture of 40 kg of PhOH and 8 kg of titanium tetrachloride was heatedto and maintained at 50° C. for 10 hours under a flow of nitrogen gas,thereby performing a reaction. After that period of time, hydrogenchloride formed in the resultant reaction mixture was distilled offtogether with unreacted PhOH. Then, most of the remaining PhOH wasdistilled off from the reaction mixture under reduced pressure, and theresultant mixture was allowed to cool in a nitrogen atmosphere, tothereby obtain catalyst III.

Production of Aromatic Carbonate

Substantially the same procedure as in Example 5 was repeated, exceptthat catalyst III was used in an amount such that the Ti concentrationof the reaction mixture in conduit 13 became 0.2% by weight. Theoperation was continued for 2,000 hours. During the 2,000 hour operationtime, the operation could be stably conducted (for example, both theflow and the composition in each conduit were stable) without sufferingdisadvantageous phenomena, such as the deposition of the catalyst from acatalyst-containing liquid and the adherence of the deposited catalystto the inside surfaces associated with the equipment employed for theoperation. From the evaporation-concentrated liquid which was formed inevaporator 14 and which contained the catalyst and high boiling pointsubstances, samples were taken through the sampling nozzle provided onconduit 15′, wherein the samples were, respectively, withdrawn at pointsin time of 1,000 hours, 1,500 hours and 2,000 hours after the start ofthe operation. The determination of the total concentration of the highboiling point substances in each sample was conducted by theabove-mentioned method. With respect to these samples withdrawn atpoints in time of 1,000 hours, 1,500 hours and 2,000 hours after thestart of the operation, the total concentrations of the high boilingpoint substances were 2.8% by weight, 2.9% by weight and 2.9% by weight,respectively. During the operation, samples of the reaction mixturewithdrawn from the bottom of reaction vessel 100 were taken through thesampling nozzle provided on conduit 13, and the samples were analyzed.With respect to the reaction mixture which was taken from conduit 13 ata point in time of 2,000 hours after the start of the operation, thecomposition of the reaction mixture was as follows: PhOH: 51% by weight;methyl phenyl carbonate (MPC): 6% by weight; diphenyl carbonate (DPC):0.4% by weight; anisole (ANS): 0.4% by weight; and Ti: 0.2% by weight.The purity of the aromatic carbonate (which was a mixture of MPC andDPC) in the condensate withdrawn from condenser 22 through conduit 23was 99.99% or more, and no high boiling point substance was detected inthe condensate. After the operation was terminated, the inside surfacesassociated with the equipment employed for the operation were examined.No adherence of the catalyst to any of the inner walls of reactionvessel 100, evaporator 14, reboiler 17, conduits and the like wasobserved.

EXAMPLE 7

235 g of diphenyl carbonate obtained in Example 3 and 228 g of bisphenolA were placed in a vacuum reaction apparatus equipped with an agitator,and the resultant mixture was heated to 180° C. while stirring andgradually evacuating the reaction apparatus with nitrogen gas. Then, thetemperature of the mixture was slowly elevated from 180 to 220° C. whilestirring and evacuating the reaction apparatus with nitrogen gas.Subsequently, the reaction apparatus was sealed, and a polymerizationwas effected at 8,000 Pa for 30 minutes while stirring at 100 rpm, andthen, at 4,000 Pa for 90 minutes while stirring at 100 rpm. Thereafter,the temperature of the reaction apparatus was elevated to 270° C., and apolymerization was effected at 70 Pa for one hour, thereby obtaining anaromatic polycarbonate. The obtained aromatic polycarbonate wascolorless and transparent, and had a number average molecular weight of10,200.

Comparative Example 5

Substantially the same procedure as in Example 7 was repeated, exceptthat the diphenyl carbonate obtained in Comparative Example 4 was used(instead of the diphenyl carbonate obtained in Example 3). The obtainedaromatic polycarbonate had suffered yellowing and had a number averagemolecular weight of 8,800.

INDUSTRIAL APPLICABILITY

By the process of the present invention, an aromatic carbonate havinghigh purity can be produced stably for a prolonged period of time.Therefore, the process of the present invention can be advantageouslyemployed in a commercial-scale mass production of an aromatic carbonate.An aromatic carbonate produced by the process of the present inventionis used as a raw material for producing aromatic polycarbonates, use ofwhich as engineering plastics has been increasing in recent years.

What is claimed is:
 1. In a process for producing aromatic carbonates,which comprises the steps of: (1) transesterifying a starting materialselected from the group consisting of a dialkyl carbonate represented bythe formula (1)

an alkyl aryl carbonate represented by the formula (2)

and a mixture thereof with a reactant selected from the group consistingof an aromatic monohydroxy compound represented by the formula (3)Ar¹OH  (3), an alkyl aryl carbonate represented by the formula (4)

and a mixture thereof, wherein each of R¹, R² and R³ independentlyrepresents an alkyl group having 1 to 10 carbon atoms, an alicyclicgroup having 3 to 10 carbon atoms or an aralkyl group having 6 to 10carbon atoms, and each of Ar¹, Ar² and Ar³ independently represents anaromatic group having 5 to 30 carbon atoms, in the presence of ametal-containing catalyst which is soluble in a reaction systemcomprising said starting material and said reactant and which is presentin a state dissolved in said reaction system, to thereby obtain a highboiling point reaction mixture comprising said metal-containing catalystand at least one aromatic carbonate which is produced by thetransesterification and which corresponds to the starting material andthe reactant and is selected from the group consisting of an alkyl arylcarbonate represented by the formula (5)

and a diaryl carbonate represented by the formula (6)

wherein R and Ar are, respectively, selected from the group consistingof R¹, R² and R³ and selected from the group consisting of Ar¹, Ar² andAr³ in correspondence to the starting material and the reactant, whilewithdrawing a low boiling point reaction mixture which contains a lowboiling point by-product comprising an aliphatic alcohol, a dialkylcarbonate or a mixture thereof corresponding to the starting materialand the reactant and represented by at least one formula selected fromthe group consisting of ROH and

wherein R is as defined above, (2) separating said high boiling pointreaction mixture into a product fraction comprising said producedaromatic carbonate and a liquid catalyst fraction comprising saidmetal-containing catalyst, and (3) recycling said liquid catalystfraction to said reaction system while withdrawing said productfraction, the improvement which comprises the steps of: (1′) taking outat least one type of catalyst-containing liquid which is selected fromthe group consisting of: a portion of said high boiling point reactionmixture before the separation of said high boiling point reactionmixture into said product fraction and said liquid catalyst fraction,and a portion of the separated liquid catalyst fraction, each portioncontaining (A) at least one high boiling point substance having aboiling point higher than the boiling point of said produced aromaticcarbonate and containing (B) said metal-containing catalyst, (2′) addingto the taken-out catalyst-containing liquid a functional substance (C)capable of reacting with at least one component selected from the groupconsisting of said component (A) and said component (B), to therebyobtain a reaction mixture containing an (A)/(C) reaction product and a(B)/(C) reaction product, wherein: when said functional substance (C) iscapable of reacting with said component (A), said (A)/(C) reactionproduct is a product formed by the reaction between said component (A)and said component (C), when said functional substance (C) is notcapable of reacting with said component (A), said (A)/(C) reactionproduct is unreacted component (A) present in said reaction mixture,when said functional substance (C) is capable of reacting with saidcomponent (B), said (B)/(C) reaction product is a product formed by thereaction between said component (B) and said component (C), and whensaid functional substance (C) is not capable of reacting with saidcomponent (B), said (B)/(C) reaction product is unreacted component (B)present in said reaction mixture, and (3′) recycling said (B)/(C)reaction product to said reaction system directly or indirectly, whilewithdrawing said (A)/(C) reaction product.
 2. The process according toclaim 1, wherein said portion of the high boiling point reaction mixtureis from 0.01 to 10% by weight, based on the weight of said high boilingpoint reaction mixture, and wherein said portion of the separated liquidcatalyst fraction is from 0.01 to 40% by weight, based on the weight ofsaid separated liquid catalyst fraction.
 3. The process according toclaim 1 or 2, wherein said high boiling point substance (A) originatesfrom at least one compound selected from the group consisting of saidstarting material, said reactant, impurities contained in said startingmaterial and said reactant, and by-products of the transesterificationreaction.
 4. The process according to claim 1 or 2, wherein said highboiling point substance (A) is at least one substance selected from thegroup consisting of an aromatic hydroxy compound (7), a compound (8)derived from said compound (7), an aromatic carboxy compound (9), acompound (10) derived from said compound (9), and xanthone, wherein:compound (7) is represented by the formula (7):

wherein Ar⁴ represents an aromatic group having a valence of m, mrepresents an integer of 2 or more, and each —OH group is independentlybonded to an arbitrary ring-carbon position of the Ar⁴ group, compound(8) contains a residue represented by the formula (8):

wherein Ar⁴ and m are as defined for formula (7), n represents aninteger of from 1 to m, and each of the -OH group and the —O— group isindependently bonded to an arbitrary ring-carbon position of the Ar⁴group, compound (9) is represented by the formula (9):

wherein Ar⁵ represents an aromatic group having a valence of r, rrepresents an integer of 1 or more, s represents an integer of from O to(r−1), and each of the —OH group and the —COOH group is independentlybonded to an arbitrary ring-carbon position of the Ar⁵ group, andcompound (10) contains a residue represented by the formula (10):

wherein Ar⁵, r and s are as defined for formula (9), t is an integer offrom O to s, u is an integer of from O to (r—s), with the proviso that tand u are not simultaneously O, and each of the —OH group, the —COOHgroup, the —O— group and the —(COO)— group is independently bonded to anarbitrary ring-carbon position of the Ar⁵ group.
 5. The processaccording to claim 1 or 2, wherein said functional substance (C) is anoxidizing agent, so that said (A)/(C) reaction product is a low boilingpoint oxidation product and said (B)/(C) reaction product is a metaloxide.
 6. The process according to claim 1 or 2, wherein said functionalsubstance (C) is a precipitant, so that said (B)/(C) reaction product isa metal-containing substance which precipitates.
 7. The processaccording to claim 6, wherein said metal-containing substance is a metalcompound selected from the group consisting of a metal carbonate, ametal hydroxide, a metal oxide, a metal sulfide and a metal sulfate. 8.The process according to claim 1 or 2, wherein said functional substance(C) is a reactive solvent, so that said (A)/(C) reaction product is alow boiling point product obtained by the solvolysis of component (A).9. The process according to claim 8, wherein said reactive solvent iswater, so that said (A)/(C) reaction product is an aromatic monohydroxycompound obtained by the hydrolysis of component (A).
 10. The processaccording to claim 1 or 2, wherein said steps (1), (2) and (3) arecontinuously performed, thereby continuously producing an aromaticcarbonate.
 11. The process according to claim 10, wherein said startingmaterial and said reactant are continuously fed to a continuousmulti-stage distillation column to effect a transesterification reactiontherebetween in at least one phase selected from the group consisting ofa liquid phase and a gas-liquid phase in the presence of saidmetal-containing catalyst in said distillation column, whilecontinuously withdrawing a high boiling point reaction mixturecontaining the produced aromatic carbonate in a liquid form from a lowerportion of the distillation column and continuously withdrawing a lowboiling point reaction mixture containing the low boiling pointby-product in a gaseous form from an upper portion of the distillationcolumn by distillation.
 12. A process for producing aromaticpolycarbonates, which comprises subjecting to transesterification nopolymerization an aromatic carbonate produced by the process accordingto any one of claims 1 to 11 and an aromatic dihydroxy compound.